<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2024 Workiva-->
<!--r:5f0beb76-c462-4d89-ae2a-52a70e7621b8,g:d95b66ff-5274-4b3e-bcec-8483479991b7-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://pubmatic.com/role/Cover" xlink:type="simple" xlink:href="pubm-20240331.xsd#Cover"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_6613a64a-eaa4-4eba-977e-05dc3bb5027b" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_DocumentInformationTable_6613a64a-eaa4-4eba-977e-05dc3bb5027b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_b482ed39-3dd2-421e-a8d6-d0adc70d788e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_6613a64a-eaa4-4eba-977e-05dc3bb5027b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_b482ed39-3dd2-421e-a8d6-d0adc70d788e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_b482ed39-3dd2-421e-a8d6-d0adc70d788e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_b482ed39-3dd2-421e-a8d6-d0adc70d788e" xlink:to="loc_us-gaap_ClassOfStockDomain_b482ed39-3dd2-421e-a8d6-d0adc70d788e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_4b6b24c0-2fbf-4323-90f8-6a28747989ed" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_b482ed39-3dd2-421e-a8d6-d0adc70d788e" xlink:to="loc_us-gaap_ClassOfStockDomain_4b6b24c0-2fbf-4323-90f8-6a28747989ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_cb0a63d2-70c0-4bd5-8d45-23bac3784586" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_4b6b24c0-2fbf-4323-90f8-6a28747989ed" xlink:to="loc_us-gaap_CommonClassAMember_cb0a63d2-70c0-4bd5-8d45-23bac3784586" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_0cee9fa6-9476-4841-b902-3889642a025e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_4b6b24c0-2fbf-4323-90f8-6a28747989ed" xlink:to="loc_us-gaap_CommonClassBMember_0cee9fa6-9476-4841-b902-3889642a025e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_67e3ab11-4974-4f0a-a73e-a1bbeb9ff313" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_DocumentType_67e3ab11-4974-4f0a-a73e-a1bbeb9ff313" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_06a7eaf7-1c8e-4f48-b540-27ca959b3a19" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_DocumentQuarterlyReport_06a7eaf7-1c8e-4f48-b540-27ca959b3a19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_3d265a7f-598b-497b-8704-32ce069c07ab" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_DocumentPeriodEndDate_3d265a7f-598b-497b-8704-32ce069c07ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_2d900584-d012-43f6-902b-31b802a40061" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_DocumentTransitionReport_2d900584-d012-43f6-902b-31b802a40061" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_24e9839b-663f-4afe-9adf-4004f426f5f2" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityFileNumber_24e9839b-663f-4afe-9adf-4004f426f5f2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_35f45cd1-0271-492e-905b-6f987c1d2ff3" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityRegistrantName_35f45cd1-0271-492e-905b-6f987c1d2ff3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_02127444-a0cf-47d0-aeb7-adefc48be835" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityIncorporationStateCountryCode_02127444-a0cf-47d0-aeb7-adefc48be835" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_0c314851-502c-4d33-8250-da46b93a848e" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityTaxIdentificationNumber_0c314851-502c-4d33-8250-da46b93a848e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_952332ce-1dcf-4e4a-9d56-0a0e43f8e7b7" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_Security12bTitle_952332ce-1dcf-4e4a-9d56-0a0e43f8e7b7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_4c6aed91-edae-4858-b12b-7b924323f2a4" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_TradingSymbol_4c6aed91-edae-4858-b12b-7b924323f2a4" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_05462fdc-1782-4275-8d70-b742e0fb9755" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_SecurityExchangeName_05462fdc-1782-4275-8d70-b742e0fb9755" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_a01d2815-23d1-4479-af27-d76245a59506" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityCurrentReportingStatus_a01d2815-23d1-4479-af27-d76245a59506" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_4bdf2362-3fcc-4857-b10c-deded598de06" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityInteractiveDataCurrent_4bdf2362-3fcc-4857-b10c-deded598de06" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_8eea04f9-822e-40e7-a822-6c9ecf6d55ef" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityFilerCategory_8eea04f9-822e-40e7-a822-6c9ecf6d55ef" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_7e58e5ac-eebf-4a00-8d3d-bd438c040163" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntitySmallBusiness_7e58e5ac-eebf-4a00-8d3d-bd438c040163" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_c16bc60e-e9fd-459f-a680-62e47cc825b9" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityEmergingGrowthCompany_c16bc60e-e9fd-459f-a680-62e47cc825b9" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_d3bbabf2-1bf4-4824-a2bc-fd61a8576387" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityShellCompany_d3bbabf2-1bf4-4824-a2bc-fd61a8576387" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_19a1c600-2471-4a50-b6eb-234f9b6a12a6" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_19a1c600-2471-4a50-b6eb-234f9b6a12a6" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_2741033a-50a3-44ef-b014-e23f941f9edc" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_AmendmentFlag_2741033a-50a3-44ef-b014-e23f941f9edc" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_1ea304f9-4de3-485e-8657-090333a6d5f6" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_EntityCentralIndexKey_1ea304f9-4de3-485e-8657-090333a6d5f6" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_4a85051f-08fd-40e0-b2ec-f636b165bf2b" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_CurrentFiscalYearEndDate_4a85051f-08fd-40e0-b2ec-f636b165bf2b" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_f51a860e-f054-4a16-8ba7-9e5f0761145e" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_DocumentFiscalYearFocus_f51a860e-f054-4a16-8ba7-9e5f0761145e" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_4ad65e63-cd87-4f8e-85c1-dec96db14a7f" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_26ab4cee-79ea-42db-9158-d1509ffc2ff6" xlink:to="loc_dei_DocumentFiscalPeriodFocus_4ad65e63-cd87-4f8e-85c1-dec96db14a7f" xlink:type="arc" order="22"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="pubm-20240331.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_f1298da1-c5cf-49c5-af3f-d5b0c096c8a1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:to="loc_us-gaap_StatementTable_f1298da1-c5cf-49c5-af3f-d5b0c096c8a1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_41d51388-763b-42c4-a42b-d5e11bfcd866" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_f1298da1-c5cf-49c5-af3f-d5b0c096c8a1" xlink:to="loc_us-gaap_StatementClassOfStockAxis_41d51388-763b-42c4-a42b-d5e11bfcd866" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_41d51388-763b-42c4-a42b-d5e11bfcd866_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_41d51388-763b-42c4-a42b-d5e11bfcd866" xlink:to="loc_us-gaap_ClassOfStockDomain_41d51388-763b-42c4-a42b-d5e11bfcd866_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_7af45171-5d04-4473-a9ee-7d15381d5719" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_41d51388-763b-42c4-a42b-d5e11bfcd866" xlink:to="loc_us-gaap_ClassOfStockDomain_7af45171-5d04-4473-a9ee-7d15381d5719" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_c1c46f9f-fcd6-45f1-ae77-889cbe4a4960" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7af45171-5d04-4473-a9ee-7d15381d5719" xlink:to="loc_us-gaap_CommonClassAMember_c1c46f9f-fcd6-45f1-ae77-889cbe4a4960" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_c525a180-d353-4aff-94f6-04400e431798" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7af45171-5d04-4473-a9ee-7d15381d5719" xlink:to="loc_us-gaap_CommonClassBMember_c525a180-d353-4aff-94f6-04400e431798" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_1602141d-7a72-4715-b7ef-d38f557532ab" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_1602141d-7a72-4715-b7ef-d38f557532ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_1a6946e8-1c2f-4dd9-8c61-e3d4f83f1d5e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_1a6946e8-1c2f-4dd9-8c61-e3d4f83f1d5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_827a27fd-754f-427a-87a9-035d647e39ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:to="loc_us-gaap_PreferredStockSharesIssued_827a27fd-754f-427a-87a9-035d647e39ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_2106e3bc-90df-4824-9e01-b1d3c88167ce" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_2106e3bc-90df-4824-9e01-b1d3c88167ce" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_5aa18b9f-737f-4d55-9ba6-302a60d9c218" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_5aa18b9f-737f-4d55-9ba6-302a60d9c218" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_d7217b3a-e032-4967-8dee-e67e187c9a19" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_d7217b3a-e032-4967-8dee-e67e187c9a19" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_b064c1ca-1318-4e2b-98c7-f62037df3733" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:to="loc_us-gaap_CommonStockSharesIssued_b064c1ca-1318-4e2b-98c7-f62037df3733" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_98053e1b-0357-49d3-ab20-0ab4ca0921dc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_98053e1b-0357-49d3-ab20-0ab4ca0921dc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_6f297c2e-6c74-4da7-a90b-7696a6c2ab66" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0f37e394-5431-478e-ba3e-924981822ba2" xlink:to="loc_us-gaap_TreasuryStockCommonShares_6f297c2e-6c74-4da7-a90b-7696a6c2ab66" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="pubm-20240331.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_391244b3-f440-4799-b1e3-1769f64655f9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_35c06f1e-f0b8-4039-ab78-6856c6285261" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_391244b3-f440-4799-b1e3-1769f64655f9" xlink:to="loc_us-gaap_StatementTable_35c06f1e-f0b8-4039-ab78-6856c6285261" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_71bc73b1-888f-4a37-b2fa-6385a1195f43" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_35c06f1e-f0b8-4039-ab78-6856c6285261" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_71bc73b1-888f-4a37-b2fa-6385a1195f43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_71bc73b1-888f-4a37-b2fa-6385a1195f43_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_71bc73b1-888f-4a37-b2fa-6385a1195f43" xlink:to="loc_us-gaap_EquityComponentDomain_71bc73b1-888f-4a37-b2fa-6385a1195f43_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_c2d49ba7-e8b1-4e13-bc5c-42f23ccd5029" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_71bc73b1-888f-4a37-b2fa-6385a1195f43" xlink:to="loc_us-gaap_EquityComponentDomain_c2d49ba7-e8b1-4e13-bc5c-42f23ccd5029" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_2ece8df9-095e-4d36-8cc4-bbb7f0a33c21" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_c2d49ba7-e8b1-4e13-bc5c-42f23ccd5029" xlink:to="loc_us-gaap_CommonStockMember_2ece8df9-095e-4d36-8cc4-bbb7f0a33c21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_0485d77f-552f-4ce3-85f7-eab78cddaf10" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_c2d49ba7-e8b1-4e13-bc5c-42f23ccd5029" xlink:to="loc_us-gaap_TreasuryStockCommonMember_0485d77f-552f-4ce3-85f7-eab78cddaf10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_87aae6fa-2428-4b2c-a01d-e9201db2e8ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_c2d49ba7-e8b1-4e13-bc5c-42f23ccd5029" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_87aae6fa-2428-4b2c-a01d-e9201db2e8ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_394b8f49-bc10-46ed-96d2-e70708e3922d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_c2d49ba7-e8b1-4e13-bc5c-42f23ccd5029" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_394b8f49-bc10-46ed-96d2-e70708e3922d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_1a230a2b-d416-451e-8a48-0aaa8aaf41c5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_c2d49ba7-e8b1-4e13-bc5c-42f23ccd5029" xlink:to="loc_us-gaap_RetainedEarningsMember_1a230a2b-d416-451e-8a48-0aaa8aaf41c5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_391244b3-f440-4799-b1e3-1769f64655f9" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_4f1196cb-3d04-4b29-ad05-57b6e64243a4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:to="loc_us-gaap_SharesOutstanding_4f1196cb-3d04-4b29-ad05-57b6e64243a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_42bab085-383c-4697-9cf7-7d94fb578dab" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:to="loc_us-gaap_StockholdersEquity_42bab085-383c-4697-9cf7-7d94fb578dab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_c96ee589-a33b-41f0-9357-463962e614ce" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_c96ee589-a33b-41f0-9357-463962e614ce" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_ab1fddb6-301d-48df-8b48-1f305c17b0e0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_ab1fddb6-301d-48df-8b48-1f305c17b0e0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_367d3b51-f9e4-417e-9624-8f16e5765c09" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_367d3b51-f9e4-417e-9624-8f16e5765c09" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_83471623-58a8-44e3-9c58-5b614e923c4b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_83471623-58a8-44e3-9c58-5b614e923c4b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_4b99e9c0-b45c-4996-a091-53d195d492d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_4b99e9c0-b45c-4996-a091-53d195d492d8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_aea0f5d7-05db-4e83-ade9-6bccb976feb3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_aea0f5d7-05db-4e83-ade9-6bccb976feb3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_bc1b6ec8-74aa-479e-9c80-79ab51ade2ad" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_bc1b6ec8-74aa-479e-9c80-79ab51ade2ad" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_cec1952b-3488-4da7-9d0c-3b714c310f73" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fd44dbdf-1e1b-480e-9ed3-2b7d9fad630b" xlink:to="loc_us-gaap_NetIncomeLoss_cec1952b-3488-4da7-9d0c-3b714c310f73" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_e04c3d13-a11e-4f55-894f-f9a58092e184" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_30194bde-a495-4245-9a6f-c32772a60bd1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesConcentrationRiskPercentageDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesConcentrationRiskPercentageDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesConcentrationRiskPercentageDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_fe8a530d-61d1-4df8-83da-f0b97137ac19" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_9c94b6e0-55f4-454a-8fc7-d5425fb8eb2e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_fe8a530d-61d1-4df8-83da-f0b97137ac19" xlink:to="loc_us-gaap_ConcentrationRiskTable_9c94b6e0-55f4-454a-8fc7-d5425fb8eb2e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_12cb46bd-c17e-49f2-8031-418b90c334f6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_9c94b6e0-55f4-454a-8fc7-d5425fb8eb2e" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_12cb46bd-c17e-49f2-8031-418b90c334f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_12cb46bd-c17e-49f2-8031-418b90c334f6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_12cb46bd-c17e-49f2-8031-418b90c334f6" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_12cb46bd-c17e-49f2-8031-418b90c334f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_b3c37dc8-66cd-4169-a466-88343bd43293" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_12cb46bd-c17e-49f2-8031-418b90c334f6" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_b3c37dc8-66cd-4169-a466-88343bd43293" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_6c5b0eeb-bf20-4ac1-af7e-21a4a3256a95" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_b3c37dc8-66cd-4169-a466-88343bd43293" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_6c5b0eeb-bf20-4ac1-af7e-21a4a3256a95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_14112c91-4251-4ce2-a833-31831d869d6a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_9c94b6e0-55f4-454a-8fc7-d5425fb8eb2e" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_14112c91-4251-4ce2-a833-31831d869d6a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_14112c91-4251-4ce2-a833-31831d869d6a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_14112c91-4251-4ce2-a833-31831d869d6a" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_14112c91-4251-4ce2-a833-31831d869d6a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_954c4c54-c26c-4134-816a-ad3e2aa6e969" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_14112c91-4251-4ce2-a833-31831d869d6a" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_954c4c54-c26c-4134-816a-ad3e2aa6e969" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_e4a10efe-533d-4b3c-aae6-f8c80ca227c9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_954c4c54-c26c-4134-816a-ad3e2aa6e969" xlink:to="loc_us-gaap_SalesRevenueNetMember_e4a10efe-533d-4b3c-aae6-f8c80ca227c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_0ae70d28-ede4-4bc9-b779-c8eba485987b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_954c4c54-c26c-4134-816a-ad3e2aa6e969" xlink:to="loc_us-gaap_AccountsReceivableMember_0ae70d28-ede4-4bc9-b779-c8eba485987b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_3bf9e903-1328-4fd8-8194-8d0e231844e3" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_9c94b6e0-55f4-454a-8fc7-d5425fb8eb2e" xlink:to="loc_srt_MajorCustomersAxis_3bf9e903-1328-4fd8-8194-8d0e231844e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_3bf9e903-1328-4fd8-8194-8d0e231844e3_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_3bf9e903-1328-4fd8-8194-8d0e231844e3" xlink:to="loc_srt_NameOfMajorCustomerDomain_3bf9e903-1328-4fd8-8194-8d0e231844e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_16a1f417-8a2a-417d-9217-49b06904faa4" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_3bf9e903-1328-4fd8-8194-8d0e231844e3" xlink:to="loc_srt_NameOfMajorCustomerDomain_16a1f417-8a2a-417d-9217-49b06904faa4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_BuyerOneMember_06e99fe4-30c2-4470-9eca-8a1ef24516e5" xlink:href="pubm-20240331.xsd#pubm_BuyerOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_16a1f417-8a2a-417d-9217-49b06904faa4" xlink:to="loc_pubm_BuyerOneMember_06e99fe4-30c2-4470-9eca-8a1ef24516e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_BuyerTwoMember_17c252c1-e100-4b1b-98cd-bbef22a400b5" xlink:href="pubm-20240331.xsd#pubm_BuyerTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_16a1f417-8a2a-417d-9217-49b06904faa4" xlink:to="loc_pubm_BuyerTwoMember_17c252c1-e100-4b1b-98cd-bbef22a400b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_BuyerThreeMember_4d2e1902-ab2f-4298-85fb-4c9251097aa3" xlink:href="pubm-20240331.xsd#pubm_BuyerThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_16a1f417-8a2a-417d-9217-49b06904faa4" xlink:to="loc_pubm_BuyerThreeMember_4d2e1902-ab2f-4298-85fb-4c9251097aa3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_OnePublisherMember_a226404c-1029-49bf-81a7-2210bd9e4600" xlink:href="pubm-20240331.xsd#pubm_OnePublisherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_16a1f417-8a2a-417d-9217-49b06904faa4" xlink:to="loc_pubm_OnePublisherMember_a226404c-1029-49bf-81a7-2210bd9e4600" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_ef853e53-e6b8-40b8-9420-522083077767" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_fe8a530d-61d1-4df8-83da-f0b97137ac19" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_ef853e53-e6b8-40b8-9420-522083077767" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/FairValueMeasurementsDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#FairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/FairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_e5cc0fdc-807b-4921-80da-63eaa39ae605" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_aa47607c-955c-4437-b4a7-136f90f8d471" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_e5cc0fdc-807b-4921-80da-63eaa39ae605" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_aa47607c-955c-4437-b4a7-136f90f8d471" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_8ebf0546-0919-4232-a060-a1bb65edba06" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_aa47607c-955c-4437-b4a7-136f90f8d471" xlink:to="loc_us-gaap_FinancialInstrumentAxis_8ebf0546-0919-4232-a060-a1bb65edba06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_8ebf0546-0919-4232-a060-a1bb65edba06_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_8ebf0546-0919-4232-a060-a1bb65edba06" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_8ebf0546-0919-4232-a060-a1bb65edba06_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a63984a1-4322-41c7-aa41-0684b8f59fc0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_8ebf0546-0919-4232-a060-a1bb65edba06" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a63984a1-4322-41c7-aa41-0684b8f59fc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_6a4f7009-d578-469a-a962-9c3c44f6f76a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a63984a1-4322-41c7-aa41-0684b8f59fc0" xlink:to="loc_us-gaap_CommercialPaperMember_6a4f7009-d578-469a-a962-9c3c44f6f76a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_9eedf7b3-379d-464f-9de2-1e794ae94389" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a63984a1-4322-41c7-aa41-0684b8f59fc0" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_9eedf7b3-379d-464f-9de2-1e794ae94389" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_982e7702-5157-49c4-8cbe-a5e0d8d2a012" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a63984a1-4322-41c7-aa41-0684b8f59fc0" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_982e7702-5157-49c4-8cbe-a5e0d8d2a012" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f9d4a807-7844-49c7-9351-1f22b594161e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_aa47607c-955c-4437-b4a7-136f90f8d471" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f9d4a807-7844-49c7-9351-1f22b594161e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f9d4a807-7844-49c7-9351-1f22b594161e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f9d4a807-7844-49c7-9351-1f22b594161e" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f9d4a807-7844-49c7-9351-1f22b594161e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_008a5d28-6d36-4612-8d35-9ab9fa3b7d57" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_f9d4a807-7844-49c7-9351-1f22b594161e" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_008a5d28-6d36-4612-8d35-9ab9fa3b7d57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_8ffa81d3-6a4f-41db-ae95-be189014751d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_008a5d28-6d36-4612-8d35-9ab9fa3b7d57" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_8ffa81d3-6a4f-41db-ae95-be189014751d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_580843e9-f30e-4f98-92a2-e335b6513e58" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_008a5d28-6d36-4612-8d35-9ab9fa3b7d57" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_580843e9-f30e-4f98-92a2-e335b6513e58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_ca0986d3-dcc8-45f1-992b-197e4d271121" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_008a5d28-6d36-4612-8d35-9ab9fa3b7d57" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_ca0986d3-dcc8-45f1-992b-197e4d271121" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_f969d44c-f31b-40a4-820c-8622a99dd843" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_aa47607c-955c-4437-b4a7-136f90f8d471" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_f969d44c-f31b-40a4-820c-8622a99dd843" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_f969d44c-f31b-40a4-820c-8622a99dd843_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_f969d44c-f31b-40a4-820c-8622a99dd843" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_f969d44c-f31b-40a4-820c-8622a99dd843_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e722ffd7-a33d-491a-a77a-45cc08e8f070" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_f969d44c-f31b-40a4-820c-8622a99dd843" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e722ffd7-a33d-491a-a77a-45cc08e8f070" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashEquivalentsMember_8c37399e-223e-406d-b9c4-8b3f2e03385b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e722ffd7-a33d-491a-a77a-45cc08e8f070" xlink:to="loc_us-gaap_CashEquivalentsMember_8c37399e-223e-406d-b9c4-8b3f2e03385b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_ee57d989-6a3c-4219-ac2b-a8c41241fdb6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashEquivalentsMember_8c37399e-223e-406d-b9c4-8b3f2e03385b" xlink:to="loc_us-gaap_MoneyMarketFundsMember_ee57d989-6a3c-4219-ac2b-a8c41241fdb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_3be0778e-b5fe-4865-9584-f0fddaf5c329" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashEquivalentsMember_8c37399e-223e-406d-b9c4-8b3f2e03385b" xlink:to="loc_us-gaap_CommercialPaperMember_3be0778e-b5fe-4865-9584-f0fddaf5c329" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CertificatesOfDepositMember_a8eed444-276a-4ed0-bab7-2be680cac147" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CertificatesOfDepositMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashEquivalentsMember_8c37399e-223e-406d-b9c4-8b3f2e03385b" xlink:to="loc_us-gaap_CertificatesOfDepositMember_a8eed444-276a-4ed0-bab7-2be680cac147" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_536c91a8-d59b-43d5-84f0-06ca3ddd830e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_aa47607c-955c-4437-b4a7-136f90f8d471" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_536c91a8-d59b-43d5-84f0-06ca3ddd830e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_536c91a8-d59b-43d5-84f0-06ca3ddd830e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_536c91a8-d59b-43d5-84f0-06ca3ddd830e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_536c91a8-d59b-43d5-84f0-06ca3ddd830e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_644d5f85-b552-41c8-bbc0-dc6255d16bea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_536c91a8-d59b-43d5-84f0-06ca3ddd830e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_644d5f85-b552-41c8-bbc0-dc6255d16bea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_a9ac6b66-3e41-40e2-a01a-09864cb4e0fb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_644d5f85-b552-41c8-bbc0-dc6255d16bea" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_a9ac6b66-3e41-40e2-a01a-09864cb4e0fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_380757d8-5670-4280-90d4-aa1ebfec7e58" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_e5cc0fdc-807b-4921-80da-63eaa39ae605" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_380757d8-5670-4280-90d4-aa1ebfec7e58" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_84b6b7be-b6b5-4596-b0db-94860aebd317" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_e5cc0fdc-807b-4921-80da-63eaa39ae605" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_84b6b7be-b6b5-4596-b0db-94860aebd317" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_865b50e6-9953-4597-9fa6-48e8ddb59790" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_e5cc0fdc-807b-4921-80da-63eaa39ae605" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_865b50e6-9953-4597-9fa6-48e8ddb59790" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/BalanceSheetComponentsSummaryofMarketableSecuritiesDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#BalanceSheetComponentsSummaryofMarketableSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/BalanceSheetComponentsSummaryofMarketableSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1f5deb2b-f77d-4556-be72-249b1b962a38" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_43fd745b-7fc0-4f6c-aa92-e7f5b583bb20" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1f5deb2b-f77d-4556-be72-249b1b962a38" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_43fd745b-7fc0-4f6c-aa92-e7f5b583bb20" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_2f6c1ba5-4e9b-4330-a82f-0438cec83baa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_43fd745b-7fc0-4f6c-aa92-e7f5b583bb20" xlink:to="loc_us-gaap_FinancialInstrumentAxis_2f6c1ba5-4e9b-4330-a82f-0438cec83baa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2f6c1ba5-4e9b-4330-a82f-0438cec83baa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_2f6c1ba5-4e9b-4330-a82f-0438cec83baa" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2f6c1ba5-4e9b-4330-a82f-0438cec83baa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6c9e94d9-9e74-424f-bb0f-f4793b1d6fef" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_2f6c1ba5-4e9b-4330-a82f-0438cec83baa" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6c9e94d9-9e74-424f-bb0f-f4793b1d6fef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_b9b68aba-c65e-43fa-b455-1b49cb1e7341" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6c9e94d9-9e74-424f-bb0f-f4793b1d6fef" xlink:to="loc_us-gaap_CommercialPaperMember_b9b68aba-c65e-43fa-b455-1b49cb1e7341" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_0d127bbd-436d-4438-afaa-877549cacdf0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6c9e94d9-9e74-424f-bb0f-f4793b1d6fef" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_0d127bbd-436d-4438-afaa-877549cacdf0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_db30f0a6-9f05-4d49-a0ae-1f4a1ff87300" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6c9e94d9-9e74-424f-bb0f-f4793b1d6fef" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_db30f0a6-9f05-4d49-a0ae-1f4a1ff87300" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostCurrent_2c24e20f-628d-44d3-b603-3dd11d6744d0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1f5deb2b-f77d-4556-be72-249b1b962a38" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostCurrent_2c24e20f-628d-44d3-b603-3dd11d6744d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_57e7a299-1012-4951-b9dc-2109b44c919e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1f5deb2b-f77d-4556-be72-249b1b962a38" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_57e7a299-1012-4951-b9dc-2109b44c919e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_c6b6338e-15c3-4a82-a4e5-e6e280efe62a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1f5deb2b-f77d-4556-be72-249b1b962a38" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_c6b6338e-15c3-4a82-a4e5-e6e280efe62a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_27c499d8-0621-49e0-97e2-5dc2b9861ebb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_1f5deb2b-f77d-4556-be72-249b1b962a38" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_27c499d8-0621-49e0-97e2-5dc2b9861ebb" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/BalanceSheetComponentsScheduleofPropertyEquipmentandSoftwareNetDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#BalanceSheetComponentsScheduleofPropertyEquipmentandSoftwareNetDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/BalanceSheetComponentsScheduleofPropertyEquipmentandSoftwareNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_b197585d-c0ff-49ca-93d1-9319c7541b9b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_81c1545d-c472-407a-ba84-8fc77f1ef1c9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_b197585d-c0ff-49ca-93d1-9319c7541b9b" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_81c1545d-c472-407a-ba84-8fc77f1ef1c9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_22824e9b-eed5-4329-a527-611b9c0269a5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_81c1545d-c472-407a-ba84-8fc77f1ef1c9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_22824e9b-eed5-4329-a527-611b9c0269a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_22824e9b-eed5-4329-a527-611b9c0269a5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_22824e9b-eed5-4329-a527-611b9c0269a5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_22824e9b-eed5-4329-a527-611b9c0269a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2895b6b8-1821-4e81-97a8-1b03f5f6520f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_22824e9b-eed5-4329-a527-611b9c0269a5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2895b6b8-1821-4e81-97a8-1b03f5f6520f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_f744dccb-cf98-43d5-bba9-ee3fd1bada57" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2895b6b8-1821-4e81-97a8-1b03f5f6520f" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_f744dccb-cf98-43d5-bba9-ee3fd1bada57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyEquipmentMember_a070c581-5c43-4883-b576-2a16c3b77bb8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TechnologyEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2895b6b8-1821-4e81-97a8-1b03f5f6520f" xlink:to="loc_us-gaap_TechnologyEquipmentMember_a070c581-5c43-4883-b576-2a16c3b77bb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_c66d2823-4a8b-4497-98d2-973061bc8d72" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2895b6b8-1821-4e81-97a8-1b03f5f6520f" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_c66d2823-4a8b-4497-98d2-973061bc8d72" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_dc5b90fc-85da-4b67-8da1-7d37990b78ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2895b6b8-1821-4e81-97a8-1b03f5f6520f" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_dc5b90fc-85da-4b67-8da1-7d37990b78ba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_52ebe9a1-1143-4e9c-9127-8a898236bc9b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_b197585d-c0ff-49ca-93d1-9319c7541b9b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_52ebe9a1-1143-4e9c-9127-8a898236bc9b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_020c8318-0ade-49be-9b01-0d9566b7f4c9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_b197585d-c0ff-49ca-93d1-9319c7541b9b" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_020c8318-0ade-49be-9b01-0d9566b7f4c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_d47093e7-9217-448a-aa0a-c1b88f413921" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_b197585d-c0ff-49ca-93d1-9319c7541b9b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_d47093e7-9217-448a-aa0a-c1b88f413921" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/BalanceSheetComponentsNarrativeDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#BalanceSheetComponentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/BalanceSheetComponentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1f4f8586-3b72-4d6f-897d-7a9bf786b757" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_411beddf-5f8d-4158-8544-1a795804f25f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1f4f8586-3b72-4d6f-897d-7a9bf786b757" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_411beddf-5f8d-4158-8544-1a795804f25f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d90226b2-fd3d-4e97-b42f-912b2c42d1ee" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_411beddf-5f8d-4158-8544-1a795804f25f" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d90226b2-fd3d-4e97-b42f-912b2c42d1ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_d90226b2-fd3d-4e97-b42f-912b2c42d1ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d90226b2-fd3d-4e97-b42f-912b2c42d1ee" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_d90226b2-fd3d-4e97-b42f-912b2c42d1ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ac07c119-9ce0-487c-b94a-a64e64b250e4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d90226b2-fd3d-4e97-b42f-912b2c42d1ee" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ac07c119-9ce0-487c-b94a-a64e64b250e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_d2a4b8f9-37e5-4827-9f02-c00a1809e420" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ac07c119-9ce0-487c-b94a-a64e64b250e4" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_d2a4b8f9-37e5-4827-9f02-c00a1809e420" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_5dff312d-e94e-4706-a715-0a1452f2c29c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1f4f8586-3b72-4d6f-897d-7a9bf786b757" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_5dff312d-e94e-4706-a715-0a1452f2c29c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareAdditions_60a4298c-ec3b-4751-b58e-2ac162c085d7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CapitalizedComputerSoftwareAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1f4f8586-3b72-4d6f-897d-7a9bf786b757" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareAdditions_60a4298c-ec3b-4751-b58e-2ac162c085d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentForAmortization_611b6c42-cbed-432d-9739-ca3d2673fb1d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentForAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1f4f8586-3b72-4d6f-897d-7a9bf786b757" xlink:to="loc_us-gaap_AdjustmentForAmortization_611b6c42-cbed-432d-9739-ca3d2673fb1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareImpairments1_7fa9af3c-cde7-404e-9651-c861bad6fce6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CapitalizedComputerSoftwareImpairments1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1f4f8586-3b72-4d6f-897d-7a9bf786b757" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareImpairments1_7fa9af3c-cde7-404e-9651-c861bad6fce6" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/SeniorSecuredCreditFacilitiesAgreementDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#SeniorSecuredCreditFacilitiesAgreementDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/SeniorSecuredCreditFacilitiesAgreementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_d092030c-bc87-4a7f-b5c5-aecdcdb595d9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_b56f5e9a-f20f-4c3e-80d1-fa4cbaf5f9fa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_d092030c-bc87-4a7f-b5c5-aecdcdb595d9" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_b56f5e9a-f20f-4c3e-80d1-fa4cbaf5f9fa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_1b9e44be-cfdd-461a-b23e-0ec54d16fef0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_b56f5e9a-f20f-4c3e-80d1-fa4cbaf5f9fa" xlink:to="loc_us-gaap_CreditFacilityAxis_1b9e44be-cfdd-461a-b23e-0ec54d16fef0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_1b9e44be-cfdd-461a-b23e-0ec54d16fef0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_1b9e44be-cfdd-461a-b23e-0ec54d16fef0" xlink:to="loc_us-gaap_CreditFacilityDomain_1b9e44be-cfdd-461a-b23e-0ec54d16fef0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_1749d574-1dfa-4ce3-904e-94a99052ac02" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_1b9e44be-cfdd-461a-b23e-0ec54d16fef0" xlink:to="loc_us-gaap_CreditFacilityDomain_1749d574-1dfa-4ce3-904e-94a99052ac02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_b84a8c83-512b-4c49-9965-dcdc5413d285" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_1749d574-1dfa-4ce3-904e-94a99052ac02" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_b84a8c83-512b-4c49-9965-dcdc5413d285" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_2baa4dd9-04d5-4aaf-87ff-a62f0691b561" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_b56f5e9a-f20f-4c3e-80d1-fa4cbaf5f9fa" xlink:to="loc_us-gaap_DebtInstrumentAxis_2baa4dd9-04d5-4aaf-87ff-a62f0691b561" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_2baa4dd9-04d5-4aaf-87ff-a62f0691b561_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_2baa4dd9-04d5-4aaf-87ff-a62f0691b561" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_2baa4dd9-04d5-4aaf-87ff-a62f0691b561_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_eaa5c7d5-d42c-406e-8a89-a5271a525b44" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_2baa4dd9-04d5-4aaf-87ff-a62f0691b561" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_eaa5c7d5-d42c-406e-8a89-a5271a525b44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_CreditAgreementMember_2b46c401-855c-4f24-8bce-636603c50504" xlink:href="pubm-20240331.xsd#pubm_CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_eaa5c7d5-d42c-406e-8a89-a5271a525b44" xlink:to="loc_pubm_CreditAgreementMember_2b46c401-855c-4f24-8bce-636603c50504" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_f0a6c950-e015-459d-9cdd-512c5580dcc3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_b56f5e9a-f20f-4c3e-80d1-fa4cbaf5f9fa" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_f0a6c950-e015-459d-9cdd-512c5580dcc3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_f0a6c950-e015-459d-9cdd-512c5580dcc3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_f0a6c950-e015-459d-9cdd-512c5580dcc3" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_f0a6c950-e015-459d-9cdd-512c5580dcc3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_2545ddb1-ca57-426f-80ee-4c9be4de566c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_f0a6c950-e015-459d-9cdd-512c5580dcc3" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_2545ddb1-ca57-426f-80ee-4c9be4de566c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_1c6421b4-2395-41cc-916f-0cfb4a94f67f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_2545ddb1-ca57-426f-80ee-4c9be4de566c" xlink:to="loc_us-gaap_LineOfCreditMember_1c6421b4-2395-41cc-916f-0cfb4a94f67f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_1ec28b25-6d03-47c5-9974-958e2b56e60b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_2545ddb1-ca57-426f-80ee-4c9be4de566c" xlink:to="loc_us-gaap_LetterOfCreditMember_1ec28b25-6d03-47c5-9974-958e2b56e60b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_SwinglineSubFacilityMember_9c5413cc-96eb-4c82-b4c0-eaf67c4a64e5" xlink:href="pubm-20240331.xsd#pubm_SwinglineSubFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_2545ddb1-ca57-426f-80ee-4c9be4de566c" xlink:to="loc_pubm_SwinglineSubFacilityMember_9c5413cc-96eb-4c82-b4c0-eaf67c4a64e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_5548cfa0-4f8f-4ce0-bd63-d577a0d46e29" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_b56f5e9a-f20f-4c3e-80d1-fa4cbaf5f9fa" xlink:to="loc_us-gaap_VariableRateAxis_5548cfa0-4f8f-4ce0-bd63-d577a0d46e29" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_5548cfa0-4f8f-4ce0-bd63-d577a0d46e29_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_5548cfa0-4f8f-4ce0-bd63-d577a0d46e29" xlink:to="loc_us-gaap_VariableRateDomain_5548cfa0-4f8f-4ce0-bd63-d577a0d46e29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_2ac37aa4-c5af-45a2-a3ab-e37679589cd8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_5548cfa0-4f8f-4ce0-bd63-d577a0d46e29" xlink:to="loc_us-gaap_VariableRateDomain_2ac37aa4-c5af-45a2-a3ab-e37679589cd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsEffectiveSwapRateMember_0f1f4d00-56be-4a0b-80f0-d4049176c2a5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FederalFundsEffectiveSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_2ac37aa4-c5af-45a2-a3ab-e37679589cd8" xlink:to="loc_us-gaap_FederalFundsEffectiveSwapRateMember_0f1f4d00-56be-4a0b-80f0-d4049176c2a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_SecuredOvernightFinancingRateSOFRMember_94f10e94-0490-4417-895d-1d7fb833ff08" xlink:href="pubm-20240331.xsd#pubm_SecuredOvernightFinancingRateSOFRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_2ac37aa4-c5af-45a2-a3ab-e37679589cd8" xlink:to="loc_pubm_SecuredOvernightFinancingRateSOFRMember_94f10e94-0490-4417-895d-1d7fb833ff08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_AlternateBaseRateMember_e886234e-c2d0-4dbd-bb9b-bef55ae6ae26" xlink:href="pubm-20240331.xsd#pubm_AlternateBaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_2ac37aa4-c5af-45a2-a3ab-e37679589cd8" xlink:to="loc_pubm_AlternateBaseRateMember_e886234e-c2d0-4dbd-bb9b-bef55ae6ae26" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_ApplicableInterestRateMember_e0146715-653e-4f7c-ae4f-1f2725393085" xlink:href="pubm-20240331.xsd#pubm_ApplicableInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_2ac37aa4-c5af-45a2-a3ab-e37679589cd8" xlink:to="loc_pubm_ApplicableInterestRateMember_e0146715-653e-4f7c-ae4f-1f2725393085" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_a4d3ca5d-d4f1-4691-8f6b-bb13975f23d4" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_b56f5e9a-f20f-4c3e-80d1-fa4cbaf5f9fa" xlink:to="loc_srt_RangeAxis_a4d3ca5d-d4f1-4691-8f6b-bb13975f23d4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_a4d3ca5d-d4f1-4691-8f6b-bb13975f23d4_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_a4d3ca5d-d4f1-4691-8f6b-bb13975f23d4" xlink:to="loc_srt_RangeMember_a4d3ca5d-d4f1-4691-8f6b-bb13975f23d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_259a73e1-2ccd-4e77-b4d8-b4962a04dc7a" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_a4d3ca5d-d4f1-4691-8f6b-bb13975f23d4" xlink:to="loc_srt_RangeMember_259a73e1-2ccd-4e77-b4d8-b4962a04dc7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_98631c39-9944-4589-ab64-22d92497b6d5" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_259a73e1-2ccd-4e77-b4d8-b4962a04dc7a" xlink:to="loc_srt_MinimumMember_98631c39-9944-4589-ab64-22d92497b6d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_d3b80447-dae3-4d11-a029-8db2d64d43ea" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_259a73e1-2ccd-4e77-b4d8-b4962a04dc7a" xlink:to="loc_srt_MaximumMember_d3b80447-dae3-4d11-a029-8db2d64d43ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_1c69cfa1-853f-457c-bffc-1a905e4d8536" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_d092030c-bc87-4a7f-b5c5-aecdcdb595d9" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_1c69cfa1-853f-457c-bffc-1a905e4d8536" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_LineOfCreditFacilityAccordionFeatureIncreaseLimit_acfc9305-a13f-4ec4-8ee7-56a0e1cc1b44" xlink:href="pubm-20240331.xsd#pubm_LineOfCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_d092030c-bc87-4a7f-b5c5-aecdcdb595d9" xlink:to="loc_pubm_LineOfCreditFacilityAccordionFeatureIncreaseLimit_acfc9305-a13f-4ec4-8ee7-56a0e1cc1b44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_7f824817-04c4-4ffb-8ece-c27f57d6142e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_d092030c-bc87-4a7f-b5c5-aecdcdb595d9" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_7f824817-04c4-4ffb-8ece-c27f57d6142e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_65614db4-1d5b-49b3-9c6e-d7cb740a49ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_d092030c-bc87-4a7f-b5c5-aecdcdb595d9" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_65614db4-1d5b-49b3-9c6e-d7cb740a49ba" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/AcquisitionrelatedIntangibleAssetsNetAcquisitionRelatedIntangibleAssetsNetDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#AcquisitionrelatedIntangibleAssetsNetAcquisitionRelatedIntangibleAssetsNetDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/AcquisitionrelatedIntangibleAssetsNetAcquisitionRelatedIntangibleAssetsNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_8e98fc6b-6882-4e53-9a57-da95be712f9a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_08645952-1867-437c-9345-b529456a0ae7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_8e98fc6b-6882-4e53-9a57-da95be712f9a" xlink:to="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_08645952-1867-437c-9345-b529456a0ae7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a5f1374d-6fec-4acd-85c9-c8ffc7203761" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_08645952-1867-437c-9345-b529456a0ae7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a5f1374d-6fec-4acd-85c9-c8ffc7203761" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a5f1374d-6fec-4acd-85c9-c8ffc7203761_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a5f1374d-6fec-4acd-85c9-c8ffc7203761" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a5f1374d-6fec-4acd-85c9-c8ffc7203761_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e228a8a3-73cf-43c7-88d8-59ae84285080" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a5f1374d-6fec-4acd-85c9-c8ffc7203761" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e228a8a3-73cf-43c7-88d8-59ae84285080" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_2d70dab3-cf9f-4c24-a3ea-753eeb4f0f0d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e228a8a3-73cf-43c7-88d8-59ae84285080" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_2d70dab3-cf9f-4c24-a3ea-753eeb4f0f0d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_0196f81b-d5c4-4fe0-9165-88d6b5ff2ddb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e228a8a3-73cf-43c7-88d8-59ae84285080" xlink:to="loc_us-gaap_CustomerRelationshipsMember_0196f81b-d5c4-4fe0-9165-88d6b5ff2ddb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_76afb515-aaf4-4fb4-a2d8-d7984e8883f8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_8e98fc6b-6882-4e53-9a57-da95be712f9a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_76afb515-aaf4-4fb4-a2d8-d7984e8883f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_07100c7f-60f9-4f04-9862-1df2ae4b5285" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_8e98fc6b-6882-4e53-9a57-da95be712f9a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_07100c7f-60f9-4f04-9862-1df2ae4b5285" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_55f56d6e-4548-42c0-a43d-dc093bede712" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_8e98fc6b-6882-4e53-9a57-da95be712f9a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_55f56d6e-4548-42c0-a43d-dc093bede712" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/AcquisitionrelatedIntangibleAssetsNetNarrativeDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#AcquisitionrelatedIntangibleAssetsNetNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/AcquisitionrelatedIntangibleAssetsNetNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_7c7a1966-5227-4970-8fc7-40453bcc2e62" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_c3603d48-2eb0-4a41-add2-4ce51a52762a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_7c7a1966-5227-4970-8fc7-40453bcc2e62" xlink:to="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_c3603d48-2eb0-4a41-add2-4ce51a52762a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3c76a6e6-9f65-4057-8336-e12297cb937c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_c3603d48-2eb0-4a41-add2-4ce51a52762a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3c76a6e6-9f65-4057-8336-e12297cb937c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c76a6e6-9f65-4057-8336-e12297cb937c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3c76a6e6-9f65-4057-8336-e12297cb937c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c76a6e6-9f65-4057-8336-e12297cb937c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d7a3ac4d-f2ce-48fe-af6f-21c9fd0dbf7b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3c76a6e6-9f65-4057-8336-e12297cb937c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d7a3ac4d-f2ce-48fe-af6f-21c9fd0dbf7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_f6fe4c05-c598-4601-9407-310b74166403" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d7a3ac4d-f2ce-48fe-af6f-21c9fd0dbf7b" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_f6fe4c05-c598-4601-9407-310b74166403" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_ab44c458-6035-43a3-9612-6abf1c5241e2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_7c7a1966-5227-4970-8fc7-40453bcc2e62" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_ab44c458-6035-43a3-9612-6abf1c5241e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_295f8d8f-e3d8-4e5f-b056-09eb12d10378" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_7c7a1966-5227-4970-8fc7-40453bcc2e62" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_295f8d8f-e3d8-4e5f-b056-09eb12d10378" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#CommitmentsandContingenciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_84e5be4d-654a-4237-ac85-81adaa0dcadf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsTable_43a892dc-6275-4562-a57a-de81bf76a4a4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_84e5be4d-654a-4237-ac85-81adaa0dcadf" xlink:to="loc_us-gaap_OtherCommitmentsTable_43a892dc-6275-4562-a57a-de81bf76a4a4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_ca69fedc-0a95-4fa0-afd8-c915a6fbf736" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_43a892dc-6275-4562-a57a-de81bf76a4a4" xlink:to="loc_us-gaap_DebtInstrumentAxis_ca69fedc-0a95-4fa0-afd8-c915a6fbf736" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ca69fedc-0a95-4fa0-afd8-c915a6fbf736_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_ca69fedc-0a95-4fa0-afd8-c915a6fbf736" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ca69fedc-0a95-4fa0-afd8-c915a6fbf736_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_bc75566f-04bc-4139-80e2-c9ed67554c89" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_ca69fedc-0a95-4fa0-afd8-c915a6fbf736" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_bc75566f-04bc-4139-80e2-c9ed67554c89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_IrrevocableLettersOfCreditDueJuly2028Member_3071404f-08ad-4836-a490-1a45ab25c862" xlink:href="pubm-20240331.xsd#pubm_IrrevocableLettersOfCreditDueJuly2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_bc75566f-04bc-4139-80e2-c9ed67554c89" xlink:to="loc_pubm_IrrevocableLettersOfCreditDueJuly2028Member_3071404f-08ad-4836-a490-1a45ab25c862" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_IrrevocableLettersOfCreditDueApril2025Member_8a284494-001b-4ce8-91e4-8c6196c7ea95" xlink:href="pubm-20240331.xsd#pubm_IrrevocableLettersOfCreditDueApril2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_bc75566f-04bc-4139-80e2-c9ed67554c89" xlink:to="loc_pubm_IrrevocableLettersOfCreditDueApril2025Member_8a284494-001b-4ce8-91e4-8c6196c7ea95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_NumberOfDebtInstruments_0f03cf41-489e-4d83-aea2-ea1d41f4bfc5" xlink:href="pubm-20240331.xsd#pubm_NumberOfDebtInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_84e5be4d-654a-4237-ac85-81adaa0dcadf" xlink:to="loc_pubm_NumberOfDebtInstruments_0f03cf41-489e-4d83-aea2-ea1d41f4bfc5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_673ee8d2-f534-4fda-81de-a72e8468cee4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_84e5be4d-654a-4237-ac85-81adaa0dcadf" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_673ee8d2-f534-4fda-81de-a72e8468cee4" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/StockholdersEquityandStockOptionPlansNarrativeDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#StockholdersEquityandStockOptionPlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/StockholdersEquityandStockOptionPlansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_4604c117-3b74-453b-8c95-9b44a0312bb6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_4604c117-3b74-453b-8c95-9b44a0312bb6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareRepurchaseProgramAxis_1bf4fd53-3806-48a4-8377-c3738f2e024f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_4604c117-3b74-453b-8c95-9b44a0312bb6" xlink:to="loc_us-gaap_ShareRepurchaseProgramAxis_1bf4fd53-3806-48a4-8377-c3738f2e024f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareRepurchaseProgramDomain_1bf4fd53-3806-48a4-8377-c3738f2e024f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareRepurchaseProgramAxis_1bf4fd53-3806-48a4-8377-c3738f2e024f" xlink:to="loc_us-gaap_ShareRepurchaseProgramDomain_1bf4fd53-3806-48a4-8377-c3738f2e024f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareRepurchaseProgramDomain_b2f89042-27cd-4c1c-a018-994514080cc9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareRepurchaseProgramAxis_1bf4fd53-3806-48a4-8377-c3738f2e024f" xlink:to="loc_us-gaap_ShareRepurchaseProgramDomain_b2f89042-27cd-4c1c-a018-994514080cc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_A2023RepurchaseProgramMember_efc64648-58ef-4d54-ad1d-0538cf0cb00c" xlink:href="pubm-20240331.xsd#pubm_A2023RepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareRepurchaseProgramDomain_b2f89042-27cd-4c1c-a018-994514080cc9" xlink:to="loc_pubm_A2023RepurchaseProgramMember_efc64648-58ef-4d54-ad1d-0538cf0cb00c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_A2024RepurchaseProgramMember_b699dd45-e82a-4cd8-b409-0ed599cf7279" xlink:href="pubm-20240331.xsd#pubm_A2024RepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareRepurchaseProgramDomain_b2f89042-27cd-4c1c-a018-994514080cc9" xlink:to="loc_pubm_A2024RepurchaseProgramMember_b699dd45-e82a-4cd8-b409-0ed599cf7279" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_526bb6c2-4b79-4fdc-a618-0a11628b9ca6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_4604c117-3b74-453b-8c95-9b44a0312bb6" xlink:to="loc_us-gaap_StatementClassOfStockAxis_526bb6c2-4b79-4fdc-a618-0a11628b9ca6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_526bb6c2-4b79-4fdc-a618-0a11628b9ca6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_526bb6c2-4b79-4fdc-a618-0a11628b9ca6" xlink:to="loc_us-gaap_ClassOfStockDomain_526bb6c2-4b79-4fdc-a618-0a11628b9ca6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_3a7b2233-9bc8-4aa5-856e-0e7c05129658" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_526bb6c2-4b79-4fdc-a618-0a11628b9ca6" xlink:to="loc_us-gaap_ClassOfStockDomain_3a7b2233-9bc8-4aa5-856e-0e7c05129658" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_bcda0d60-f638-43f1-a697-3c26b47daba6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_3a7b2233-9bc8-4aa5-856e-0e7c05129658" xlink:to="loc_us-gaap_CommonClassAMember_bcda0d60-f638-43f1-a697-3c26b47daba6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_1046cf10-67d5-4d71-8acd-0d9159f66f3d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_4604c117-3b74-453b-8c95-9b44a0312bb6" xlink:to="loc_us-gaap_AwardTypeAxis_1046cf10-67d5-4d71-8acd-0d9159f66f3d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1046cf10-67d5-4d71-8acd-0d9159f66f3d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_1046cf10-67d5-4d71-8acd-0d9159f66f3d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1046cf10-67d5-4d71-8acd-0d9159f66f3d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_15f3bbbd-d368-4385-b26c-7502018122a8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_1046cf10-67d5-4d71-8acd-0d9159f66f3d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_15f3bbbd-d368-4385-b26c-7502018122a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_af508e12-19f3-421a-9624-ff4004abbacb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_15f3bbbd-d368-4385-b26c-7502018122a8" xlink:to="loc_us-gaap_EmployeeStockOptionMember_af508e12-19f3-421a-9624-ff4004abbacb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_02bb72fd-5e35-4f7d-b29a-ef3eb4de18ed" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_15f3bbbd-d368-4385-b26c-7502018122a8" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_02bb72fd-5e35-4f7d-b29a-ef3eb4de18ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_9358d2c0-fcac-4947-ac86-5ed886c9f8ab" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_15f3bbbd-d368-4385-b26c-7502018122a8" xlink:to="loc_us-gaap_EmployeeStockMember_9358d2c0-fcac-4947-ac86-5ed886c9f8ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_575f5757-d3eb-408c-a1c1-bcbf0464231c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_575f5757-d3eb-408c-a1c1-bcbf0464231c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_b9a323f7-c360-42c2-a17d-82299f33f046" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_b9a323f7-c360-42c2-a17d-82299f33f046" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_71ae7b8f-0203-473f-a3a2-d61db3787589" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_71ae7b8f-0203-473f-a3a2-d61db3787589" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_f026d3b3-d987-48a3-9364-98f960f9b88e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_f026d3b3-d987-48a3-9364-98f960f9b88e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_ec624680-ddc3-469b-8b6f-94039c8c48a1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_ec624680-ddc3-469b-8b6f-94039c8c48a1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_ShareBasedCompensationArrangementAutomaticAnnualIncreaseTerm_e2980054-22d2-464b-ad8a-c2217ce972be" xlink:href="pubm-20240331.xsd#pubm_ShareBasedCompensationArrangementAutomaticAnnualIncreaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_pubm_ShareBasedCompensationArrangementAutomaticAnnualIncreaseTerm_e2980054-22d2-464b-ad8a-c2217ce972be" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_30c57dcd-0784-4c20-abd0-36c777ccc369" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_30c57dcd-0784-4c20-abd0-36c777ccc369" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_20e8146d-f801-4f36-945a-a3f9c16ab926" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_20e8146d-f801-4f36-945a-a3f9c16ab926" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_21c357cb-e128-47c1-96fb-b31024be4c25" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_21c357cb-e128-47c1-96fb-b31024be4c25" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_7df01354-6fdf-47b7-8e83-13879aa381c4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_7df01354-6fdf-47b7-8e83-13879aa381c4" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum_05959e67-059a-4fed-a0a4-c133665c117a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum_05959e67-059a-4fed-a0a4-c133665c117a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate_be856c66-6fb7-4cac-90f4-41bd4889d577" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate_be856c66-6fb7-4cac-90f4-41bd4889d577" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod_1a812a56-0c54-43fc-8033-a376b859613f" xlink:href="pubm-20240331.xsd#pubm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_pubm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod_1a812a56-0c54-43fc-8033-a376b859613f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod_0c31254c-0a1e-4a0e-8f16-840af20e7cf4" xlink:href="pubm-20240331.xsd#pubm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_pubm_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod_0c31254c-0a1e-4a0e-8f16-840af20e7cf4" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_NumberOfPurchasePeriods_e0b13d4c-1e77-47e8-9cfe-5e410c53ab86" xlink:href="pubm-20240331.xsd#pubm_NumberOfPurchasePeriods"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_pubm_NumberOfPurchasePeriods_e0b13d4c-1e77-47e8-9cfe-5e410c53ab86" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_ShareBasedCompensationArrangementByShareBasedPaymentAwardAmountWithheldForEmployeeStockPurchasePlan_d568b600-0df9-410e-85f5-f1033760c158" xlink:href="pubm-20240331.xsd#pubm_ShareBasedCompensationArrangementByShareBasedPaymentAwardAmountWithheldForEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_pubm_ShareBasedCompensationArrangementByShareBasedPaymentAwardAmountWithheldForEmployeeStockPurchasePlan_d568b600-0df9-410e-85f5-f1033760c158" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_394a392c-14d9-4ca7-b011-f604c5ea18b1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_773172d7-6f7d-4245-9410-a13aadb95c4f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_394a392c-14d9-4ca7-b011-f604c5ea18b1" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/StockholdersEquityandStockOptionPlansSummaryofRestrictedStockUnitsandRelatedInformationDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#StockholdersEquityandStockOptionPlansSummaryofRestrictedStockUnitsandRelatedInformationDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/StockholdersEquityandStockOptionPlansSummaryofRestrictedStockUnitsandRelatedInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_691a54ce-a472-4c1e-9b36-830058a9e824" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_2a7d90d6-be22-46d3-8b01-63d4e6ecde85" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_691a54ce-a472-4c1e-9b36-830058a9e824" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_2a7d90d6-be22-46d3-8b01-63d4e6ecde85" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_21c12e58-ee94-4d73-ac7a-ed1c716fd336" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_2a7d90d6-be22-46d3-8b01-63d4e6ecde85" xlink:to="loc_us-gaap_AwardTypeAxis_21c12e58-ee94-4d73-ac7a-ed1c716fd336" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_21c12e58-ee94-4d73-ac7a-ed1c716fd336_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_21c12e58-ee94-4d73-ac7a-ed1c716fd336" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_21c12e58-ee94-4d73-ac7a-ed1c716fd336_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b49068ac-6907-45cd-a841-41201e56e1d2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_21c12e58-ee94-4d73-ac7a-ed1c716fd336" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b49068ac-6907-45cd-a841-41201e56e1d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_0305fba4-7e41-4838-83b3-7a93f055114a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b49068ac-6907-45cd-a841-41201e56e1d2" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_0305fba4-7e41-4838-83b3-7a93f055114a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5d203fee-d48c-454a-8698-fd86dead7788" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_691a54ce-a472-4c1e-9b36-830058a9e824" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5d203fee-d48c-454a-8698-fd86dead7788" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_1c338a47-cca4-46fc-8afb-dafba8d05f4f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5d203fee-d48c-454a-8698-fd86dead7788" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_1c338a47-cca4-46fc-8afb-dafba8d05f4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_b03e1cca-faf6-4dbe-9448-e5a8d33adada" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5d203fee-d48c-454a-8698-fd86dead7788" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_b03e1cca-faf6-4dbe-9448-e5a8d33adada" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_9094315e-d8a0-414b-9722-e90da0e28caa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5d203fee-d48c-454a-8698-fd86dead7788" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_9094315e-d8a0-414b-9722-e90da0e28caa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_7bbe1cef-3676-45f9-9ea2-8da5722950ca" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5d203fee-d48c-454a-8698-fd86dead7788" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_7bbe1cef-3676-45f9-9ea2-8da5722950ca" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_cea61ed6-2305-44ef-97d8-9a8573c7fdfb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ca614112-8d37-4a33-82e2-70cb27981960" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_691a54ce-a472-4c1e-9b36-830058a9e824" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ca614112-8d37-4a33-82e2-70cb27981960" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_5a73ae41-f4f4-4958-a533-44b5cfa1e528" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ca614112-8d37-4a33-82e2-70cb27981960" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_5a73ae41-f4f4-4958-a533-44b5cfa1e528" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_e0cc5361-e674-4adc-bb5e-57747d0f7dd8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ca614112-8d37-4a33-82e2-70cb27981960" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_e0cc5361-e674-4adc-bb5e-57747d0f7dd8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_b56ac418-baf3-47e8-8a5c-9419415ebe26" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ca614112-8d37-4a33-82e2-70cb27981960" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_b56ac418-baf3-47e8-8a5c-9419415ebe26" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_f2f4dc59-c01b-4786-91ed-e6c01eb32a72" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ca614112-8d37-4a33-82e2-70cb27981960" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_f2f4dc59-c01b-4786-91ed-e6c01eb32a72" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_09497872-a730-48a4-9682-4c77f553f984" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/StockholdersEquityandStockOptionPlansStockbasedCompensationExpenseDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#StockholdersEquityandStockOptionPlansStockbasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/StockholdersEquityandStockOptionPlansStockbasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_1f067f3c-125f-40ad-b80f-9c6b60cb98bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_31cadafc-1457-4e86-a748-974ffb515591" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_1f067f3c-125f-40ad-b80f-9c6b60cb98bf" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_31cadafc-1457-4e86-a748-974ffb515591" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_8d788973-26c6-4d29-9acb-09685a35ab2f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_31cadafc-1457-4e86-a748-974ffb515591" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_8d788973-26c6-4d29-9acb-09685a35ab2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_8d788973-26c6-4d29-9acb-09685a35ab2f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_8d788973-26c6-4d29-9acb-09685a35ab2f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_8d788973-26c6-4d29-9acb-09685a35ab2f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_5612d112-df88-41ee-b988-0507c800fd2a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_8d788973-26c6-4d29-9acb-09685a35ab2f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_5612d112-df88-41ee-b988-0507c800fd2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_f94e85df-9331-44e4-baad-61b895264f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_5612d112-df88-41ee-b988-0507c800fd2a" xlink:to="loc_us-gaap_CostOfSalesMember_f94e85df-9331-44e4-baad-61b895264f9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_ccfa1ef6-8fe4-4c81-b1e5-397f4d038633" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_5612d112-df88-41ee-b988-0507c800fd2a" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_ccfa1ef6-8fe4-4c81-b1e5-397f4d038633" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_b92bc117-b6a2-45ca-91f8-ce3dc44fd11f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_5612d112-df88-41ee-b988-0507c800fd2a" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_b92bc117-b6a2-45ca-91f8-ce3dc44fd11f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_153d06fa-d0e6-40da-844d-000020b3f2cd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_5612d112-df88-41ee-b988-0507c800fd2a" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_153d06fa-d0e6-40da-844d-000020b3f2cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_90f3d0be-04b5-4e11-b126-b67ec6a0f85b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_1f067f3c-125f-40ad-b80f-9c6b60cb98bf" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_90f3d0be-04b5-4e11-b126-b67ec6a0f85b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_ShareBasedPaymentArrangementTaxBenefit_ef41ca5a-b2ad-4fdb-a784-2f111684ee16" xlink:href="pubm-20240331.xsd#pubm_ShareBasedPaymentArrangementTaxBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_1f067f3c-125f-40ad-b80f-9c6b60cb98bf" xlink:to="loc_pubm_ShareBasedPaymentArrangementTaxBenefit_ef41ca5a-b2ad-4fdb-a784-2f111684ee16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_ShareBasedPaymentArrangementExpenseNet_6393ca80-010e-4802-8c22-618adf403806" xlink:href="pubm-20240331.xsd#pubm_ShareBasedPaymentArrangementExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_1f067f3c-125f-40ad-b80f-9c6b60cb98bf" xlink:to="loc_pubm_ShareBasedPaymentArrangementExpenseNet_6393ca80-010e-4802-8c22-618adf403806" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/NetLossPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsperShareDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#NetLossPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsperShareDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/NetLossPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsperShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDilutedLineItems_bc6721fa-1938-4537-9389-6beaabf81972" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareDilutedLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_277fd6f9-d420-4928-a0e7-7754f6425d14" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EarningsPerShareDilutedLineItems_bc6721fa-1938-4537-9389-6beaabf81972" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_277fd6f9-d420-4928-a0e7-7754f6425d14" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_79542ae8-0763-4a5c-bc5b-8bb02e2fe92e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_277fd6f9-d420-4928-a0e7-7754f6425d14" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_79542ae8-0763-4a5c-bc5b-8bb02e2fe92e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_79542ae8-0763-4a5c-bc5b-8bb02e2fe92e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_79542ae8-0763-4a5c-bc5b-8bb02e2fe92e" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_79542ae8-0763-4a5c-bc5b-8bb02e2fe92e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d6bf710f-a5b9-4819-8253-d848429afb01" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_79542ae8-0763-4a5c-bc5b-8bb02e2fe92e" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d6bf710f-a5b9-4819-8253-d848429afb01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_7563d6a1-a24c-416c-8254-fa186b844501" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d6bf710f-a5b9-4819-8253-d848429afb01" xlink:to="loc_us-gaap_EmployeeStockOptionMember_7563d6a1-a24c-416c-8254-fa186b844501" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_681460fb-5894-4ff0-ab0f-4f6f86240cac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d6bf710f-a5b9-4819-8253-d848429afb01" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_681460fb-5894-4ff0-ab0f-4f6f86240cac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_6a781944-b924-41f6-bee2-e563d632d9cc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d6bf710f-a5b9-4819-8253-d848429afb01" xlink:to="loc_us-gaap_EmployeeStockMember_6a781944-b924-41f6-bee2-e563d632d9cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_d237ca2b-bf7c-439c-a01c-25ae0f214f1b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedLineItems_bc6721fa-1938-4537-9389-6beaabf81972" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_d237ca2b-bf7c-439c-a01c-25ae0f214f1b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://pubmatic.com/role/SegmentReportingDetails" xlink:type="simple" xlink:href="pubm-20240331.xsd#SegmentReportingDetails"/>
  <link:definitionLink xlink:role="http://pubmatic.com/role/SegmentReportingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_dff4fdaf-67c2-40cd-bb89-a3aba8d1bd14" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_61c6dc70-47f3-429c-b0df-2f2017d7c340" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_dff4fdaf-67c2-40cd-bb89-a3aba8d1bd14" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_61c6dc70-47f3-429c-b0df-2f2017d7c340" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_1103cfdb-b753-4b50-a8ad-eba14d683241" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_61c6dc70-47f3-429c-b0df-2f2017d7c340" xlink:to="loc_srt_StatementGeographicalAxis_1103cfdb-b753-4b50-a8ad-eba14d683241" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_1103cfdb-b753-4b50-a8ad-eba14d683241_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_1103cfdb-b753-4b50-a8ad-eba14d683241" xlink:to="loc_srt_SegmentGeographicalDomain_1103cfdb-b753-4b50-a8ad-eba14d683241_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_72c1ed46-62be-409d-8075-5b1884fcf12f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_1103cfdb-b753-4b50-a8ad-eba14d683241" xlink:to="loc_srt_SegmentGeographicalDomain_72c1ed46-62be-409d-8075-5b1884fcf12f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_d5b07215-ae7e-4bbe-b7bd-7cae1abd1a6d" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_72c1ed46-62be-409d-8075-5b1884fcf12f" xlink:to="loc_country_US_d5b07215-ae7e-4bbe-b7bd-7cae1abd1a6d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_d86e9af7-e968-43ba-a755-2bf9f954bf2d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EMEAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_72c1ed46-62be-409d-8075-5b1884fcf12f" xlink:to="loc_us-gaap_EMEAMember_d86e9af7-e968-43ba-a755-2bf9f954bf2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_1ad54d5f-4c55-4002-ab3b-873eb8ee3bc0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_72c1ed46-62be-409d-8075-5b1884fcf12f" xlink:to="loc_srt_AsiaPacificMember_1ad54d5f-4c55-4002-ab3b-873eb8ee3bc0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pubm_RestOfTheWorldMember_a79c844c-dacf-4bde-a669-df3e4158ee2d" xlink:href="pubm-20240331.xsd#pubm_RestOfTheWorldMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_72c1ed46-62be-409d-8075-5b1884fcf12f" xlink:to="loc_pubm_RestOfTheWorldMember_a79c844c-dacf-4bde-a669-df3e4158ee2d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_4b0ed331-d3c8-4ca2-a71d-bf78ea09a482" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_dff4fdaf-67c2-40cd-bb89-a3aba8d1bd14" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_4b0ed331-d3c8-4ca2-a71d-bf78ea09a482" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncurrentAssets_ee102998-e446-4864-83b9-f90c3a721629" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_dff4fdaf-67c2-40cd-bb89-a3aba8d1bd14" xlink:to="loc_us-gaap_NoncurrentAssets_ee102998-e446-4864-83b9-f90c3a721629" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#AwardTypeOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaap_EmployeeStockMember" xlink:type="arc" order="5"/>
  </link:definitionLink>
</link:linkbase>
