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

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2023 Workiva-->
<!--r:c2c50254-509f-4bee-97c0-565f6867a813,g:6872fe38-640b-42e9-a71b-152e3634b704-->
<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://www.comcast.com/role/DocumentandEntityInformation" xlink:type="simple" xlink:href="cmcsa-20230126.xsd#DocumentandEntityInformation"/>
  <link:definitionLink xlink:role="http://www.comcast.com/role/DocumentandEntityInformation" xlink:type="extended" id="i3be47a4496954c7aa40330bcc67f65f3_DocumentandEntityInformation">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_6fcd0e87-591f-4bca-b61f-91003c1f9c59" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_DocumentType_6fcd0e87-591f-4bca-b61f-91003c1f9c59" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_b066ba48-ce35-4b23-9eb2-d4cd3555f04d" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_AmendmentFlag_b066ba48-ce35-4b23-9eb2-d4cd3555f04d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_e82c21a4-d53b-47d8-b2f7-42c7eb43b420" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_DocumentPeriodEndDate_e82c21a4-d53b-47d8-b2f7-42c7eb43b420" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_70bce939-5f9d-4450-81cb-a4920c26c70c" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_EntityRegistrantName_70bce939-5f9d-4450-81cb-a4920c26c70c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_7e265076-5018-40b7-9d8d-a0c4867ba2d5" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_EntityCentralIndexKey_7e265076-5018-40b7-9d8d-a0c4867ba2d5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_58fdef4d-3752-4768-b838-08f781f67d39" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_EntityIncorporationStateCountryCode_58fdef4d-3752-4768-b838-08f781f67d39" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_e1d429a2-96ee-4da2-ab65-275e61225dde" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_EntityFileNumber_e1d429a2-96ee-4da2-ab65-275e61225dde" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_bd31b8a8-17f6-4f75-8576-ba9b62cf6f57" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_EntityTaxIdentificationNumber_bd31b8a8-17f6-4f75-8576-ba9b62cf6f57" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_1b9643cb-cc0d-4df2-bb03-bd34ae21bf03" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_EntityAddressAddressLine1_1b9643cb-cc0d-4df2-bb03-bd34ae21bf03" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_40f5d62a-c1fa-4461-b98e-97ce9a9d0281" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_EntityAddressCityOrTown_40f5d62a-c1fa-4461-b98e-97ce9a9d0281" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_a30e5a69-677a-4310-afe9-fdff9b37bfb6" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_EntityAddressStateOrProvince_a30e5a69-677a-4310-afe9-fdff9b37bfb6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_86eeaf79-72ea-43f9-9a37-9a875df26c63" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_EntityAddressPostalZipCode_86eeaf79-72ea-43f9-9a37-9a875df26c63" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_1b06b65f-2fa9-45ea-ad40-9a5e7618fdde" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_CityAreaCode_1b06b65f-2fa9-45ea-ad40-9a5e7618fdde" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_3de9694b-89b3-40ef-9c61-0401e790db92" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_LocalPhoneNumber_3de9694b-89b3-40ef-9c61-0401e790db92" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_79c1d689-9a7b-4569-9c4a-9c0c2fea7ca6" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_WrittenCommunications_79c1d689-9a7b-4569-9c4a-9c0c2fea7ca6" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_dd72392e-62ca-4858-a772-664bd217d9e9" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_SolicitingMaterial_dd72392e-62ca-4858-a772-664bd217d9e9" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_a137fab7-4f46-45e4-83f3-e5b7fe42c0b8" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_PreCommencementTenderOffer_a137fab7-4f46-45e4-83f3-e5b7fe42c0b8" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_1381c9d7-b668-4182-b70a-8baf17163802" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_1381c9d7-b668-4182-b70a-8baf17163802" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_73288a59-0607-4000-ab32-dc9c7a0b9d86" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_Security12bTitle_73288a59-0607-4000-ab32-dc9c7a0b9d86" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_65bfd1d7-163f-426b-95e2-936c1757bee9" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_TradingSymbol_65bfd1d7-163f-426b-95e2-936c1757bee9" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_02a44dde-abcd-474d-84a6-e44794c1f5a7" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_SecurityExchangeName_02a44dde-abcd-474d-84a6-e44794c1f5a7" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_7fcabd85-2817-4df8-9535-45ce07e04974" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_EntityEmergingGrowthCompany_7fcabd85-2817-4df8-9535-45ce07e04974" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_cb4fbf82-20e0-4f32-9ee5-ec2031727098" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_7e601124-3b45-4ab8-aeea-0dc544b500f3" xlink:to="loc_dei_DocumentInformationTable_cb4fbf82-20e0-4f32-9ee5-ec2031727098" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_db5210a5-b012-4d08-8109-fc39824d3967" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_cb4fbf82-20e0-4f32-9ee5-ec2031727098" xlink:to="loc_us-gaap_StatementClassOfStockAxis_db5210a5-b012-4d08-8109-fc39824d3967" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_db5210a5-b012-4d08-8109-fc39824d3967_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_db5210a5-b012-4d08-8109-fc39824d3967" xlink:to="loc_us-gaap_ClassOfStockDomain_db5210a5-b012-4d08-8109-fc39824d3967_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_db5210a5-b012-4d08-8109-fc39824d3967" xlink:to="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_4f8a839c-e6e3-45e6-944d-3e6a1e729843" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:to="loc_us-gaap_CommonClassAMember_4f8a839c-e6e3-45e6-944d-3e6a1e729843" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmcsa_Notes0.250percentDue2027Member_8a2e8425-2d61-46ac-8d94-d4714f6bb19a" xlink:href="cmcsa-20230126.xsd#cmcsa_Notes0.250percentDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:to="loc_cmcsa_Notes0.250percentDue2027Member_8a2e8425-2d61-46ac-8d94-d4714f6bb19a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmcsa_Notes1.500percentDue2029Member_95d9d75a-cbc4-439c-952a-12899554dd7d" xlink:href="cmcsa-20230126.xsd#cmcsa_Notes1.500percentDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:to="loc_cmcsa_Notes1.500percentDue2029Member_95d9d75a-cbc4-439c-952a-12899554dd7d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmcsa_Notes0.750percentdue2032Member_790d7df7-5e48-42a9-804f-cbd21f8f9dfd" xlink:href="cmcsa-20230126.xsd#cmcsa_Notes0.750percentdue2032Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:to="loc_cmcsa_Notes0.750percentdue2032Member_790d7df7-5e48-42a9-804f-cbd21f8f9dfd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmcsa_Notes1.875percentdue2036Member_6ddc2ef4-442b-437d-b2c9-5cea8b2bf409" xlink:href="cmcsa-20230126.xsd#cmcsa_Notes1.875percentdue2036Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:to="loc_cmcsa_Notes1.875percentdue2036Member_6ddc2ef4-442b-437d-b2c9-5cea8b2bf409" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmcsa_Notes1.250percentdue2040Member_b69a1373-d5da-4c7f-b7ed-98febc11ba36" xlink:href="cmcsa-20230126.xsd#cmcsa_Notes1.250percentdue2040Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:to="loc_cmcsa_Notes1.250percentdue2040Member_b69a1373-d5da-4c7f-b7ed-98febc11ba36" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmcsa_Notes5.50PercentDue2029Member_5597a5fe-7ce0-4ad9-990c-b1e05199add0" xlink:href="cmcsa-20230126.xsd#cmcsa_Notes5.50PercentDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:to="loc_cmcsa_Notes5.50PercentDue2029Member_5597a5fe-7ce0-4ad9-990c-b1e05199add0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmcsa_ExchangeableSubordinatedDebentures2.0PercentDue2029Member_e38a1cfa-f2f2-483c-a207-d801d3f731ac" xlink:href="cmcsa-20230126.xsd#cmcsa_ExchangeableSubordinatedDebentures2.0PercentDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:to="loc_cmcsa_ExchangeableSubordinatedDebentures2.0PercentDue2029Member_e38a1cfa-f2f2-483c-a207-d801d3f731ac" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmcsa_Notes0000PercentDue2026Member_0a531330-6d55-4e01-9a11-351d3c3bf911" xlink:href="cmcsa-20230126.xsd#cmcsa_Notes0000PercentDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:to="loc_cmcsa_Notes0000PercentDue2026Member_0a531330-6d55-4e01-9a11-351d3c3bf911" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmcsa_Notes0250PercentDue2029Member_9a959ce1-5315-49b0-9488-a681bf19e4d3" xlink:href="cmcsa-20230126.xsd#cmcsa_Notes0250PercentDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c78d22d2-e9d2-4887-a285-2afff42dfd58" xlink:to="loc_cmcsa_Notes0250PercentDue2029Member_9a959ce1-5315-49b0-9488-a681bf19e4d3" xlink:type="arc" order="9"/>
  </link:definitionLink>
</link:linkbase>
