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

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2021 Workiva-->
<!--r:3d3fa881-eb6b-47eb-b158-843a0e7a3b84,g:73bdeaa5-6ea8-4e1a-9cbe-61bb3594aa60-->
<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.harmonicinc.com/role/DocumentandEntityInformation" xlink:type="simple" xlink:href="hlit-20210402.xsd#DocumentandEntityInformation"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/DocumentandEntityInformation" xlink:type="extended" id="i78f91d8ae659409ea380d3db729769ae_DocumentandEntityInformation">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_9858227a-8d92-4a85-a1e7-1d111c554f23" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_Security12bTitle_9858227a-8d92-4a85-a1e7-1d111c554f23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_70bc4325-2c80-49f9-9ee2-63e7c8aca00d" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityIncorporationStateCountryCode_70bc4325-2c80-49f9-9ee2-63e7c8aca00d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_8ff5e527-9d3d-4934-b2bd-dd1abfc50810" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityFileNumber_8ff5e527-9d3d-4934-b2bd-dd1abfc50810" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_2d7daa2e-1462-4f92-8077-38d148642208" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_DocumentTransitionReport_2d7daa2e-1462-4f92-8077-38d148642208" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_d8f726e4-f6fc-415c-8059-98d8d0797a22" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_DocumentQuarterlyReport_d8f726e4-f6fc-415c-8059-98d8d0797a22" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_9d988d68-c17a-4443-9bd3-09c0a375322a" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_DocumentType_9d988d68-c17a-4443-9bd3-09c0a375322a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_1a744a03-8834-45af-9976-f87333ceeacb" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_AmendmentFlag_1a744a03-8834-45af-9976-f87333ceeacb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_a0f557d5-7d3f-4ed5-ac3e-fbdeafdc5aa4" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_DocumentPeriodEndDate_a0f557d5-7d3f-4ed5-ac3e-fbdeafdc5aa4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_328b3e8f-3d9b-45fc-beb8-8298206b30fe" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_DocumentFiscalYearFocus_328b3e8f-3d9b-45fc-beb8-8298206b30fe" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_18168e13-7c37-4b8e-ad80-2e38986dac9b" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_DocumentFiscalPeriodFocus_18168e13-7c37-4b8e-ad80-2e38986dac9b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_cfaeeab6-5bfe-4993-aa1e-ed4f1df72514" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityRegistrantName_cfaeeab6-5bfe-4993-aa1e-ed4f1df72514" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_d3fd4eaf-0b5a-4dfb-8cb9-fb54d9976a92" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityCentralIndexKey_d3fd4eaf-0b5a-4dfb-8cb9-fb54d9976a92" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_1ab4460f-cf9c-4b98-8752-52bb1643ad34" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_CurrentFiscalYearEndDate_1ab4460f-cf9c-4b98-8752-52bb1643ad34" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_6b0081d0-88c7-4a50-81ca-30f7ab5359fc" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityCurrentReportingStatus_6b0081d0-88c7-4a50-81ca-30f7ab5359fc" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_d0e65327-f0c8-4e29-88e0-23f90364b4dc" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityInteractiveDataCurrent_d0e65327-f0c8-4e29-88e0-23f90364b4dc" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_2810b50c-2426-41dd-94d2-5418b629118f" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityFilerCategory_2810b50c-2426-41dd-94d2-5418b629118f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_a9715383-44fc-4e57-8ec2-5ae1ecc7f610" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityShellCompany_a9715383-44fc-4e57-8ec2-5ae1ecc7f610" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_ea36f34c-3d55-49cf-9f29-276603d8f2b2" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityEmergingGrowthCompany_ea36f34c-3d55-49cf-9f29-276603d8f2b2" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_2e825171-61cb-47ba-886f-5d1bbd54db31" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntitySmallBusiness_2e825171-61cb-47ba-886f-5d1bbd54db31" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_4e4ad52f-9f79-48f2-a68d-79043071c4fa" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_4e4ad52f-9f79-48f2-a68d-79043071c4fa" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_a9ce0b8d-de70-4eea-9cc2-3ddadc2d05d3" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityTaxIdentificationNumber_a9ce0b8d-de70-4eea-9cc2-3ddadc2d05d3" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_7761d926-b96b-4f1d-a93f-8db06d7346c4" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityAddressAddressLine1_7761d926-b96b-4f1d-a93f-8db06d7346c4" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_e7908474-5f5d-4d43-8aa5-bf4066c3ae2e" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityAddressCityOrTown_e7908474-5f5d-4d43-8aa5-bf4066c3ae2e" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_b40e1048-57fd-41d4-903a-5e5ce2198d7f" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityAddressStateOrProvince_b40e1048-57fd-41d4-903a-5e5ce2198d7f" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_59188785-d847-4ea0-9f3f-b5aa0f6bca53" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_EntityAddressPostalZipCode_59188785-d847-4ea0-9f3f-b5aa0f6bca53" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_16f2e457-821c-4c36-8d78-c94286ba07a2" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_CityAreaCode_16f2e457-821c-4c36-8d78-c94286ba07a2" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_6604bfef-d854-470d-8b9e-9b7bb513375c" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_LocalPhoneNumber_6604bfef-d854-470d-8b9e-9b7bb513375c" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_a020383c-ba2b-43fa-9f5a-b5e14a2b9107" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_TradingSymbol_a020383c-ba2b-43fa-9f5a-b5e14a2b9107" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_2ce3bc32-b83f-4b52-8a8a-bfa80af48622" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_SecurityExchangeName_2ce3bc32-b83f-4b52-8a8a-bfa80af48622" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_732358d3-0ef9-484b-abfa-8525f8519954" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_718a444c-5120-44ad-89fb-a2b02057f0c8" xlink:to="loc_dei_DocumentInformationTable_732358d3-0ef9-484b-abfa-8525f8519954" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationDocumentAxis_a09de9b5-2ac1-448d-92eb-801c06016360" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentInformationDocumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_732358d3-0ef9-484b-abfa-8525f8519954" xlink:to="loc_dei_DocumentInformationDocumentAxis_a09de9b5-2ac1-448d-92eb-801c06016360" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentDomain_a09de9b5-2ac1-448d-92eb-801c06016360_default" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_DocumentInformationDocumentAxis_a09de9b5-2ac1-448d-92eb-801c06016360" xlink:to="loc_dei_DocumentDomain_a09de9b5-2ac1-448d-92eb-801c06016360_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentDomain_644d7b9b-746c-43d7-ac9a-fa1e4f89ec3d" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_DocumentInformationDocumentAxis_a09de9b5-2ac1-448d-92eb-801c06016360" xlink:to="loc_dei_DocumentDomain_644d7b9b-746c-43d7-ac9a-fa1e4f89ec3d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="hlit-20210402.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="extended" id="i9ed3cfcfbf4c45a3b9137c2179c5a9ed_CONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="hlit-20210402.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended" id="i544724f185a24695be9637692c5dfb9a_CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="simple" xlink:href="hlit-20210402.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="extended" id="ifda3e7c89f324b0e85e33992654e99d8_CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_0e0a46cc-dbf0-4b78-88aa-e9c88eb92cdb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_3dd32c68-90f8-4115-b750-f6ba8bf0d762" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0e0a46cc-dbf0-4b78-88aa-e9c88eb92cdb" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_3dd32c68-90f8-4115-b750-f6ba8bf0d762" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_1158dae5-89fa-4981-8288-ee80d0f75211" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0e0a46cc-dbf0-4b78-88aa-e9c88eb92cdb" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_1158dae5-89fa-4981-8288-ee80d0f75211" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_9211bfcb-89f7-4f51-ba11-6d1618ebe153" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_0e0a46cc-dbf0-4b78-88aa-e9c88eb92cdb" xlink:to="loc_us-gaap_StatementTable_9211bfcb-89f7-4f51-ba11-6d1618ebe153" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_3329a208-b56c-4d0c-b825-d620d8b109f3" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_9211bfcb-89f7-4f51-ba11-6d1618ebe153" xlink:to="loc_srt_ProductOrServiceAxis_3329a208-b56c-4d0c-b825-d620d8b109f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_3329a208-b56c-4d0c-b825-d620d8b109f3_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_3329a208-b56c-4d0c-b825-d620d8b109f3" xlink:to="loc_srt_ProductsAndServicesDomain_3329a208-b56c-4d0c-b825-d620d8b109f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_8647f71e-3942-455e-bf7a-b3b39c8e9ada" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_3329a208-b56c-4d0c-b825-d620d8b109f3" xlink:to="loc_srt_ProductsAndServicesDomain_8647f71e-3942-455e-bf7a-b3b39c8e9ada" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ApplianceIntegrationMember_ef66d769-38f4-45d2-af9f-823b0553025b" xlink:href="hlit-20210402.xsd#hlit_ApplianceIntegrationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8647f71e-3942-455e-bf7a-b3b39c8e9ada" xlink:to="loc_hlit_ApplianceIntegrationMember_ef66d769-38f4-45d2-af9f-823b0553025b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_SaaSServiceMember_27c13130-0173-4393-83d7-6018c0cfdd58" xlink:href="hlit-20210402.xsd#hlit_SaaSServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_8647f71e-3942-455e-bf7a-b3b39c8e9ada" xlink:to="loc_hlit_SaaSServiceMember_27c13130-0173-4393-83d7-6018c0cfdd58" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSS" xlink:type="simple" xlink:href="hlit-20210402.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSS"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSS" xlink:type="extended" id="i00084593841c458fbc970a4c6ea78a13_CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSS">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_7ec77d6d-521a-42b4-a9a8-105f5cbb5b60" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_f8a28f7f-8b93-409a-9637-c272144e4dc7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7ec77d6d-521a-42b4-a9a8-105f5cbb5b60" xlink:to="loc_us-gaap_NetIncomeLoss_f8a28f7f-8b93-409a-9637-c272144e4dc7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentAbstract_7193f85a-8935-489f-840a-d9213e09e1ab" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7ec77d6d-521a-42b4-a9a8-105f5cbb5b60" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentAbstract_7193f85a-8935-489f-840a-d9213e09e1ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossBeforeReclassificationAndTax_ee1e89f9-e5a0-4c27-a243-d8aff0dcaa66" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossBeforeReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentAbstract_7193f85a-8935-489f-840a-d9213e09e1ab" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossBeforeReclassificationAndTax_ee1e89f9-e5a0-4c27-a243-d8aff0dcaa66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_1c965a61-1e7b-4dc5-b7b8-0790d2f8adb6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentAbstract_7193f85a-8935-489f-840a-d9213e09e1ab" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_1c965a61-1e7b-4dc5-b7b8-0790d2f8adb6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTax_4f3ebf9f-7050-438b-b395-473a93a40b95" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentAbstract_7193f85a-8935-489f-840a-d9213e09e1ab" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTax_4f3ebf9f-7050-438b-b395-473a93a40b95" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_aebf877f-dae4-46da-8e64-86df41674651" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentAbstract_7193f85a-8935-489f-840a-d9213e09e1ab" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_aebf877f-dae4-46da-8e64-86df41674651" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_05fae4ce-9191-4b76-b87f-0b4ae2b27622" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentAbstract_7193f85a-8935-489f-840a-d9213e09e1ab" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_05fae4ce-9191-4b76-b87f-0b4ae2b27622" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_58a9357e-648e-45a7-98f5-67cd2b979ba3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_7ec77d6d-521a-42b4-a9a8-105f5cbb5b60" xlink:to="loc_us-gaap_StatementTable_58a9357e-648e-45a7-98f5-67cd2b979ba3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_2a0f29bd-e049-477e-9747-df8acf33d7b5" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_58a9357e-648e-45a7-98f5-67cd2b979ba3" xlink:to="loc_srt_StatementScenarioAxis_2a0f29bd-e049-477e-9747-df8acf33d7b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_2a0f29bd-e049-477e-9747-df8acf33d7b5_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_2a0f29bd-e049-477e-9747-df8acf33d7b5" xlink:to="loc_srt_ScenarioUnspecifiedDomain_2a0f29bd-e049-477e-9747-df8acf33d7b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_75dcaaf9-b67e-40cc-9cb7-646da930ebe0" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_2a0f29bd-e049-477e-9747-df8acf33d7b5" xlink:to="loc_srt_ScenarioUnspecifiedDomain_75dcaaf9-b67e-40cc-9cb7-646da930ebe0" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="hlit-20210402.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended" id="i0b5214d0d36945cabfd8d68c781168e2_CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_3c9249ff-847d-4d06-ac1f-2980d5d7620c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_SharesIssued_3c9249ff-847d-4d06-ac1f-2980d5d7620c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_7cb57ec9-2538-42b9-88b2-77fb3d53fe98" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_StockholdersEquity_7cb57ec9-2538-42b9-88b2-77fb3d53fe98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_7cf8440b-f52d-46b4-ac61-d6f7606fb003" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_NetIncomeLoss_7cf8440b-f52d-46b4-ac61-d6f7606fb003" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_5be3706c-71c9-476a-9b9b-fb572a2c1390" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_5be3706c-71c9-476a-9b9b-fb572a2c1390" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_9064a0cc-95a3-4116-a41c-e51e0d854073" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_9064a0cc-95a3-4116-a41c-e51e0d854073" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_fe464452-ab71-496c-a82e-781748ea2712" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_fe464452-ab71-496c-a82e-781748ea2712" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_3c628906-55ec-486c-b085-cb802fc1acc8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_3c628906-55ec-486c-b085-cb802fc1acc8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_b5dd9b51-317d-442b-a289-3a5d7f90362e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_b5dd9b51-317d-442b-a289-3a5d7f90362e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants_21a80707-d8a6-45fd-822b-3231628884c5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants_21a80707-d8a6-45fd-822b-3231628884c5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalOther_12cbba4e-941a-46de-a620-9836732a6840" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalOther_12cbba4e-941a-46de-a620-9836732a6840" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_AdjustmentsToAPICReclassificationFromEquityToMezzanineEquity_7ac1c3b7-28fb-46dc-8802-4e207cf29771" xlink:href="hlit-20210402.xsd#hlit_AdjustmentsToAPICReclassificationFromEquityToMezzanineEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_hlit_AdjustmentsToAPICReclassificationFromEquityToMezzanineEquity_7ac1c3b7-28fb-46dc-8802-4e207cf29771" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_AdjustmentToAPICReclassificationFromMezzanineEquityToEquity_012ccc39-737a-4b4f-a2e0-4f92584c9322" xlink:href="hlit-20210402.xsd#hlit_AdjustmentToAPICReclassificationFromMezzanineEquityToEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_hlit_AdjustmentToAPICReclassificationFromMezzanineEquityToEquity_012ccc39-737a-4b4f-a2e0-4f92584c9322" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_cac12052-a550-4e66-a6cc-19f5fd0b69f3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_a2eebac1-4fe3-4fa3-94ad-8c9c021346e0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_b077937a-1aea-47ad-9ec3-6deb0199cae0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_b4b3cc9c-2076-4c1c-b400-c451aee8cc95" xlink:to="loc_us-gaap_StatementTable_b077937a-1aea-47ad-9ec3-6deb0199cae0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_709ef281-9ebc-4715-af5f-32f52d4c0479" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_b077937a-1aea-47ad-9ec3-6deb0199cae0" xlink:to="loc_us-gaap_DebtInstrumentAxis_709ef281-9ebc-4715-af5f-32f52d4c0479" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_709ef281-9ebc-4715-af5f-32f52d4c0479_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_709ef281-9ebc-4715-af5f-32f52d4c0479" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_709ef281-9ebc-4715-af5f-32f52d4c0479_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_82fdfa46-31d0-4293-8d53-3a0523ad7d4f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_709ef281-9ebc-4715-af5f-32f52d4c0479" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_82fdfa46-31d0-4293-8d53-3a0523ad7d4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2020Member_6983e917-f2eb-46cb-8472-9555e53aa41f" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_82fdfa46-31d0-4293-8d53-3a0523ad7d4f" xlink:to="loc_hlit_ConvertibleNotedue2020Member_6983e917-f2eb-46cb-8472-9555e53aa41f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2022Member_5c296d63-244d-45fd-a372-1e1bbd64ffac" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_82fdfa46-31d0-4293-8d53-3a0523ad7d4f" xlink:to="loc_hlit_ConvertibleNotedue2022Member_5c296d63-244d-45fd-a372-1e1bbd64ffac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_1390f714-7c24-47c0-b330-12b8b62370e5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_b077937a-1aea-47ad-9ec3-6deb0199cae0" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_1390f714-7c24-47c0-b330-12b8b62370e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_1390f714-7c24-47c0-b330-12b8b62370e5_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_1390f714-7c24-47c0-b330-12b8b62370e5" xlink:to="loc_us-gaap_EquityComponentDomain_1390f714-7c24-47c0-b330-12b8b62370e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_5e087840-77d8-4cca-9314-3cf01206045f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_1390f714-7c24-47c0-b330-12b8b62370e5" xlink:to="loc_us-gaap_EquityComponentDomain_5e087840-77d8-4cca-9314-3cf01206045f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_92e10035-0d85-4cb0-b717-9b5fd532f5a0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5e087840-77d8-4cca-9314-3cf01206045f" xlink:to="loc_us-gaap_CommonStockMember_92e10035-0d85-4cb0-b717-9b5fd532f5a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_24fb4c29-5bca-45d3-ad9f-424aad8884d1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5e087840-77d8-4cca-9314-3cf01206045f" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_24fb4c29-5bca-45d3-ad9f-424aad8884d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_e185f20d-2091-46a2-b001-d7bd34ea9b11" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5e087840-77d8-4cca-9314-3cf01206045f" xlink:to="loc_us-gaap_RetainedEarningsMember_e185f20d-2091-46a2-b001-d7bd34ea9b11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_629362c2-4728-46c2-af32-eac7665a63cb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5e087840-77d8-4cca-9314-3cf01206045f" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_629362c2-4728-46c2-af32-eac7665a63cb" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS" xlink:type="simple" xlink:href="hlit-20210402.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS" xlink:type="extended" id="i347fe540c1284a599ab3eeadf6b2c667_CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/BasisofPresentationandSignificantAccountingPolicies" xlink:type="simple" xlink:href="hlit-20210402.xsd#BasisofPresentationandSignificantAccountingPolicies"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/BasisofPresentationandSignificantAccountingPolicies" xlink:type="extended" id="i1d50bf4a014e447a9936aa03f3deb724_BasisofPresentationandSignificantAccountingPolicies"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/BasisofPresentationandSignificantAccountingPoliciesPolicies" xlink:type="simple" xlink:href="hlit-20210402.xsd#BasisofPresentationandSignificantAccountingPoliciesPolicies"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/BasisofPresentationandSignificantAccountingPoliciesPolicies" xlink:type="extended" id="i67eeb530432e4f188b0472a0befaa071_BasisofPresentationandSignificantAccountingPoliciesPolicies"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/RecentAccountingPronouncements" xlink:type="simple" xlink:href="hlit-20210402.xsd#RecentAccountingPronouncements"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/RecentAccountingPronouncements" xlink:type="extended" id="if201fccdcae54295b04a8d57488b958b_RecentAccountingPronouncements"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/RecentAccountingPronouncementsAdditionalInformationDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#RecentAccountingPronouncementsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/RecentAccountingPronouncementsAdditionalInformationDetails" xlink:type="extended" id="i0877297bb65d4e808cbb1d82d1071e58_RecentAccountingPronouncementsAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_4aced9e7-3a7c-470a-aa7f-7dbb8da0cbec" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities_b7fef2d7-f7bf-4da8-9aba-7a995333aec3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4aced9e7-3a7c-470a-aa7f-7dbb8da0cbec" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities_b7fef2d7-f7bf-4da8-9aba-7a995333aec3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_4a9acf5c-06b0-4493-8721-ad4398e1dad6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4aced9e7-3a7c-470a-aa7f-7dbb8da0cbec" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_4a9acf5c-06b0-4493-8721-ad4398e1dad6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_53631538-384a-4409-a7f6-2e3b628a423c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_4a9acf5c-06b0-4493-8721-ad4398e1dad6" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_53631538-384a-4409-a7f6-2e3b628a423c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_53631538-384a-4409-a7f6-2e3b628a423c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_53631538-384a-4409-a7f6-2e3b628a423c" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_53631538-384a-4409-a7f6-2e3b628a423c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_a7b4f462-750d-4844-9355-6a32900f1208" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_53631538-384a-4409-a7f6-2e3b628a423c" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_a7b4f462-750d-4844-9355-6a32900f1208" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_14dd006f-10d4-4b93-84d5-5a1b9fecaa57" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_a7b4f462-750d-4844-9355-6a32900f1208" xlink:to="loc_us-gaap_SubsequentEventMember_14dd006f-10d4-4b93-84d5-5a1b9fecaa57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_d0d47d84-67e2-4b20-b01d-7722f16fe69a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_4a9acf5c-06b0-4493-8721-ad4398e1dad6" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_d0d47d84-67e2-4b20-b01d-7722f16fe69a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_d0d47d84-67e2-4b20-b01d-7722f16fe69a_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_d0d47d84-67e2-4b20-b01d-7722f16fe69a" xlink:to="loc_us-gaap_TypeOfAdoptionMember_d0d47d84-67e2-4b20-b01d-7722f16fe69a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_61b1c00c-234d-4cec-9f9a-e12f4fe5686c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_d0d47d84-67e2-4b20-b01d-7722f16fe69a" xlink:to="loc_us-gaap_TypeOfAdoptionMember_61b1c00c-234d-4cec-9f9a-e12f4fe5686c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_AccountingStandardsUpdate202006MemberMember_aae38b1d-97d0-4312-b0b2-2b2dee91867b" xlink:href="hlit-20210402.xsd#hlit_AccountingStandardsUpdate202006MemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_61b1c00c-234d-4cec-9f9a-e12f4fe5686c" xlink:to="loc_hlit_AccountingStandardsUpdate202006MemberMember_aae38b1d-97d0-4312-b0b2-2b2dee91867b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenue" xlink:type="simple" xlink:href="hlit-20210402.xsd#ContractAssetsandDeferredRevenue"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenue" xlink:type="extended" id="ia10dd22973e54be2bed4d8e45abd63da_ContractAssetsandDeferredRevenue"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenueTables" xlink:type="simple" xlink:href="hlit-20210402.xsd#ContractAssetsandDeferredRevenueTables"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenueTables" xlink:type="extended" id="ib173fa39c42c451dab1f30f715c759a7_ContractAssetsandDeferredRevenueTables"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenueDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#ContractAssetsandDeferredRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenueDetails" xlink:type="extended" id="i44a916b1d386491a9887c9b444f9a5d7_ContractAssetsandDeferredRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostLineItems_9dd008e4-eec0-492e-8ebe-4822df1573fd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CapitalizedContractCostLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_a45c01c8-e519-4a45-8af1-8f9adcf8932b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_9dd008e4-eec0-492e-8ebe-4822df1573fd" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_a45c01c8-e519-4a45-8af1-8f9adcf8932b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_aba6ad79-6194-43d1-849a-acd355e02f4c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_9dd008e4-eec0-492e-8ebe-4822df1573fd" xlink:to="loc_us-gaap_ContractWithCustomerLiability_aba6ad79-6194-43d1-849a-acd355e02f4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostTable_3cd42979-4887-4633-98f9-e012fe7c851e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CapitalizedContractCostTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_9dd008e4-eec0-492e-8ebe-4822df1573fd" xlink:to="loc_us-gaap_CapitalizedContractCostTable_3cd42979-4887-4633-98f9-e012fe7c851e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_6d61facf-06cd-40f0-81fe-d8c269f909a0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_3cd42979-4887-4633-98f9-e012fe7c851e" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_6d61facf-06cd-40f0-81fe-d8c269f909a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_6d61facf-06cd-40f0-81fe-d8c269f909a0_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_6d61facf-06cd-40f0-81fe-d8c269f909a0" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_6d61facf-06cd-40f0-81fe-d8c269f909a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_8c89e741-6051-4389-9093-4ba293177bb3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_6d61facf-06cd-40f0-81fe-d8c269f909a0" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_8c89e741-6051-4389-9093-4ba293177bb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_b1535e19-c276-4147-aba0-4d154193d238" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_8c89e741-6051-4389-9093-4ba293177bb3" xlink:to="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_b1535e19-c276-4147-aba0-4d154193d238" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentLiabilitiesMember_b0d2a90c-1dba-44d7-a703-1b1f75f3ba2e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherNoncurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_8c89e741-6051-4389-9093-4ba293177bb3" xlink:to="loc_us-gaap_OtherNoncurrentLiabilitiesMember_b0d2a90c-1dba-44d7-a703-1b1f75f3ba2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAxis_074ef704-f375-4cf8-9d16-dc343800a3bb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CapitalizedContractCostAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_3cd42979-4887-4633-98f9-e012fe7c851e" xlink:to="loc_us-gaap_CapitalizedContractCostAxis_074ef704-f375-4cf8-9d16-dc343800a3bb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_074ef704-f375-4cf8-9d16-dc343800a3bb_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_074ef704-f375-4cf8-9d16-dc343800a3bb" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_074ef704-f375-4cf8-9d16-dc343800a3bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_d14791df-afb3-44dc-a037-5f6deee96bb2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_074ef704-f375-4cf8-9d16-dc343800a3bb" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_d14791df-afb3-44dc-a037-5f6deee96bb2" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenueAdditionalInformationDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#ContractAssetsandDeferredRevenueAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenueAdditionalInformationDetails" xlink:type="extended" id="i21be931d4a974774b9f302d53a512e5b_ContractAssetsandDeferredRevenueAdditionalInformationDetails"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenueNarrativesDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#ContractAssetsandDeferredRevenueNarrativesDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenueNarrativesDetails" xlink:type="extended" id="i7f7fe59181154bf8b1864e489d982835_ContractAssetsandDeferredRevenueNarrativesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_5b10ca54-0011-4285-a9c7-a96103cf6581" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_7315b4a6-bf78-4946-9847-9c42b3349e6d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_5b10ca54-0011-4285-a9c7-a96103cf6581" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_7315b4a6-bf78-4946-9847-9c42b3349e6d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_eff7b84a-ecc5-41fb-b7f3-75a7b2e418e7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_5b10ca54-0011-4285-a9c7-a96103cf6581" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_eff7b84a-ecc5-41fb-b7f3-75a7b2e418e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_20025868-362c-47bf-976f-ff8736a77a4e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_5b10ca54-0011-4285-a9c7-a96103cf6581" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_20025868-362c-47bf-976f-ff8736a77a4e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_fec4322c-6c09-4cd5-b720-d2b6c781f7a2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_20025868-362c-47bf-976f-ff8736a77a4e" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_fec4322c-6c09-4cd5-b720-d2b6c781f7a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_0a482d3c-bac5-4019-9809-dcd78f0771e7" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_20025868-362c-47bf-976f-ff8736a77a4e" xlink:to="loc_srt_MajorCustomersAxis_0a482d3c-bac5-4019-9809-dcd78f0771e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_0a482d3c-bac5-4019-9809-dcd78f0771e7_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_0a482d3c-bac5-4019-9809-dcd78f0771e7" xlink:to="loc_srt_NameOfMajorCustomerDomain_0a482d3c-bac5-4019-9809-dcd78f0771e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_e2a053f8-09f4-46ac-8b48-d64d33154d1f" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_0a482d3c-bac5-4019-9809-dcd78f0771e7" xlink:to="loc_srt_NameOfMajorCustomerDomain_e2a053f8-09f4-46ac-8b48-d64d33154d1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ComcastCableOSSoftwareLicenseAgreementMember_6f6a3196-3035-4b72-8146-085f8d0831a6" xlink:href="hlit-20210402.xsd#hlit_ComcastCableOSSoftwareLicenseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_e2a053f8-09f4-46ac-8b48-d64d33154d1f" xlink:to="loc_hlit_ComcastCableOSSoftwareLicenseAgreementMember_6f6a3196-3035-4b72-8146-085f8d0831a6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenueNarrativesDetails_1" xlink:type="simple" xlink:href="hlit-20210402.xsd#ContractAssetsandDeferredRevenueNarrativesDetails_1"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ContractAssetsandDeferredRevenueNarrativesDetails_1" xlink:type="extended" id="ic2fdc72f4c844e51893a62d77bc3a81c_ContractAssetsandDeferredRevenueNarrativesDetails_1">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_5b10ca54-0011-4285-a9c7-a96103cf6581" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_7315b4a6-bf78-4946-9847-9c42b3349e6d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_5b10ca54-0011-4285-a9c7-a96103cf6581" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_7315b4a6-bf78-4946-9847-9c42b3349e6d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_eff7b84a-ecc5-41fb-b7f3-75a7b2e418e7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_5b10ca54-0011-4285-a9c7-a96103cf6581" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_eff7b84a-ecc5-41fb-b7f3-75a7b2e418e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_20025868-362c-47bf-976f-ff8736a77a4e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_5b10ca54-0011-4285-a9c7-a96103cf6581" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_20025868-362c-47bf-976f-ff8736a77a4e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_0a482d3c-bac5-4019-9809-dcd78f0771e7" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_20025868-362c-47bf-976f-ff8736a77a4e" xlink:to="loc_srt_MajorCustomersAxis_0a482d3c-bac5-4019-9809-dcd78f0771e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_0a482d3c-bac5-4019-9809-dcd78f0771e7_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_0a482d3c-bac5-4019-9809-dcd78f0771e7" xlink:to="loc_srt_NameOfMajorCustomerDomain_0a482d3c-bac5-4019-9809-dcd78f0771e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_e2a053f8-09f4-46ac-8b48-d64d33154d1f" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_0a482d3c-bac5-4019-9809-dcd78f0771e7" xlink:to="loc_srt_NameOfMajorCustomerDomain_e2a053f8-09f4-46ac-8b48-d64d33154d1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ComcastCableOSSoftwareLicenseAgreementMember_6f6a3196-3035-4b72-8146-085f8d0831a6" xlink:href="hlit-20210402.xsd#hlit_ComcastCableOSSoftwareLicenseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_e2a053f8-09f4-46ac-8b48-d64d33154d1f" xlink:to="loc_hlit_ComcastCableOSSoftwareLicenseAgreementMember_6f6a3196-3035-4b72-8146-085f8d0831a6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/Leases" xlink:type="simple" xlink:href="hlit-20210402.xsd#Leases"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/Leases" xlink:type="extended" id="i0d0411e9582c4633977111ebd7a0e3b6_Leases"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/LeaseTables" xlink:type="simple" xlink:href="hlit-20210402.xsd#LeaseTables"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/LeaseTables" xlink:type="extended" id="ic87180eeaedc45d78f8c0cb8018b6a88_LeaseTables"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/LeaseLeaseInformationDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#LeaseLeaseInformationDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/LeaseLeaseInformationDetails" xlink:type="extended" id="i0883f8ab73124294a95c63fd2ea175a7_LeaseLeaseInformationDetails"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/OtherFinancialStatementInformation" xlink:type="simple" xlink:href="hlit-20210402.xsd#OtherFinancialStatementInformation"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/OtherFinancialStatementInformation" xlink:type="extended" id="if6c0a101d9154f0d9c6f5e19670c36fd_OtherFinancialStatementInformation"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/OtherFinancialStatementInformationTables" xlink:type="simple" xlink:href="hlit-20210402.xsd#OtherFinancialStatementInformationTables"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/OtherFinancialStatementInformationTables" xlink:type="extended" id="i4eff0c236a0040d58cc126f995bc0274_OtherFinancialStatementInformationTables"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/OtherFinancialStatementInformationAccountsReceivableNetDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#OtherFinancialStatementInformationAccountsReceivableNetDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/OtherFinancialStatementInformationAccountsReceivableNetDetails" xlink:type="extended" id="id10822a151fe44e0ae961961841a6b0c_OtherFinancialStatementInformationAccountsReceivableNetDetails"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/OtherFinancialStatementInformationInventoriesnetDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#OtherFinancialStatementInformationInventoriesnetDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/OtherFinancialStatementInformationInventoriesnetDetails" xlink:type="extended" id="id9961e417ec743c2a58e640a31c14179_OtherFinancialStatementInformationInventoriesnetDetails"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/OtherFinancialStatementInformationPrepaidExpensesAndOtherCurrentAssetsDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#OtherFinancialStatementInformationPrepaidExpensesAndOtherCurrentAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/OtherFinancialStatementInformationPrepaidExpensesAndOtherCurrentAssetsDetails" xlink:type="extended" id="idda28e65609245bb87907d8abe2345c2_OtherFinancialStatementInformationPrepaidExpensesAndOtherCurrentAssetsDetails"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/OtherFinancialStatementInformationPropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#OtherFinancialStatementInformationPropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/OtherFinancialStatementInformationPropertyandEquipmentNetDetails" xlink:type="extended" id="i5050e4f2c71c4b65a76cdee447d0feb7_OtherFinancialStatementInformationPropertyandEquipmentNetDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_711409c3-2cce-49f2-b0c8-03a261c210a2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_69511b9d-d137-4775-872e-64c9cf6a61f7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_711409c3-2cce-49f2-b0c8-03a261c210a2" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_69511b9d-d137-4775-872e-64c9cf6a61f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_47593e65-63af-4557-983d-dc327d286c07" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_711409c3-2cce-49f2-b0c8-03a261c210a2" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_47593e65-63af-4557-983d-dc327d286c07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_0466a233-b2e6-4d8b-b291-306d31fc8159" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_711409c3-2cce-49f2-b0c8-03a261c210a2" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_0466a233-b2e6-4d8b-b291-306d31fc8159" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0874e813-b848-4949-aacb-123b3a0eb2a6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_711409c3-2cce-49f2-b0c8-03a261c210a2" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0874e813-b848-4949-aacb-123b3a0eb2a6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_c3ff8c80-edbb-403e-97d7-2b23a1132835" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0874e813-b848-4949-aacb-123b3a0eb2a6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_c3ff8c80-edbb-403e-97d7-2b23a1132835" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c3ff8c80-edbb-403e-97d7-2b23a1132835_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_c3ff8c80-edbb-403e-97d7-2b23a1132835" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c3ff8c80-edbb-403e-97d7-2b23a1132835_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3fecfb8f-311f-4b17-858e-423819ef0747" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_c3ff8c80-edbb-403e-97d7-2b23a1132835" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3fecfb8f-311f-4b17-858e-423819ef0747" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_4c63dbd0-e27e-4c67-8ea9-21404ea657a6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3fecfb8f-311f-4b17-858e-423819ef0747" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_4c63dbd0-e27e-4c67-8ea9-21404ea657a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_f58f731d-3365-4aec-af30-9d4318ce3aec" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3fecfb8f-311f-4b17-858e-423819ef0747" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_f58f731d-3365-4aec-af30-9d4318ce3aec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_bb8cbf46-4a1e-4ea5-8638-bee144efc23b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3fecfb8f-311f-4b17-858e-423819ef0747" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_bb8cbf46-4a1e-4ea5-8638-bee144efc23b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_d3cd63c8-c6b6-4fdc-ba3d-544dc61b1746" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3fecfb8f-311f-4b17-858e-423819ef0747" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_d3cd63c8-c6b6-4fdc-ba3d-544dc61b1746" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_9089dd04-1f9c-4bef-81dc-1a188cb49f32" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3fecfb8f-311f-4b17-858e-423819ef0747" xlink:to="loc_us-gaap_ConstructionInProgressMember_9089dd04-1f9c-4bef-81dc-1a188cb49f32" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/OtherFinancialStatementInformationOtherCurrentLiabilitiesDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#OtherFinancialStatementInformationOtherCurrentLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/OtherFinancialStatementInformationOtherCurrentLiabilitiesDetails" xlink:type="extended" id="i23fdbf0d7d5943a6867ea8c9151d8224_OtherFinancialStatementInformationOtherCurrentLiabilitiesDetails"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ConvertibleDebt" xlink:type="simple" xlink:href="hlit-20210402.xsd#ConvertibleDebt"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ConvertibleDebt" xlink:type="extended" id="ia114490810944099abf86dd0e63cbbe8_ConvertibleDebt"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ConvertibleDebtTables" xlink:type="simple" xlink:href="hlit-20210402.xsd#ConvertibleDebtTables"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ConvertibleDebtTables" xlink:type="extended" id="ifa482df9a9a34881b7d1715cce536bc6_ConvertibleDebtTables">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_1205a85d-6445-472f-bd6e-acbe55eca9d3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCarryingValuesAndEstimatedFairValuesOfDebtInstrumentsTableTextBlock_4aaccb16-c797-4218-aa5d-f93b4346f4d8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfCarryingValuesAndEstimatedFairValuesOfDebtInstrumentsTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1205a85d-6445-472f-bd6e-acbe55eca9d3" xlink:to="loc_us-gaap_ScheduleOfCarryingValuesAndEstimatedFairValuesOfDebtInstrumentsTableTextBlock_4aaccb16-c797-4218-aa5d-f93b4346f4d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtTableTextBlock_5d1b2772-f789-430a-9df1-b0df44690588" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1205a85d-6445-472f-bd6e-acbe55eca9d3" xlink:to="loc_us-gaap_ConvertibleDebtTableTextBlock_5d1b2772-f789-430a-9df1-b0df44690588" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_29977b58-4221-4427-b651-fb4c96ec0798" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1205a85d-6445-472f-bd6e-acbe55eca9d3" xlink:to="loc_us-gaap_DebtInstrumentTable_29977b58-4221-4427-b651-fb4c96ec0798" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_c04a5208-f363-4065-9f61-36a7d1ff2aa3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_29977b58-4221-4427-b651-fb4c96ec0798" xlink:to="loc_us-gaap_DebtInstrumentAxis_c04a5208-f363-4065-9f61-36a7d1ff2aa3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c04a5208-f363-4065-9f61-36a7d1ff2aa3_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_c04a5208-f363-4065-9f61-36a7d1ff2aa3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c04a5208-f363-4065-9f61-36a7d1ff2aa3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_1c74062a-8449-457a-868c-4b6f7275b84b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_c04a5208-f363-4065-9f61-36a7d1ff2aa3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_1c74062a-8449-457a-868c-4b6f7275b84b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2022Member_cbdfeac6-7973-431a-8df5-64b2df4583ed" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_1c74062a-8449-457a-868c-4b6f7275b84b" xlink:to="loc_hlit_ConvertibleNotedue2022Member_cbdfeac6-7973-431a-8df5-64b2df4583ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2024Member_d5148050-6c5d-4427-976f-63a7c5df6a1e" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_1c74062a-8449-457a-868c-4b6f7275b84b" xlink:to="loc_hlit_ConvertibleNotedue2024Member_d5148050-6c5d-4427-976f-63a7c5df6a1e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ConvertibleDebtNarrativesDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#ConvertibleDebtNarrativesDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ConvertibleDebtNarrativesDetails" xlink:type="extended" id="i0472fa66a0a641e48d0d936e2a90561e_ConvertibleDebtNarrativesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_baaa0c7f-60ee-4fa4-8b67-65e7ef10059a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_baaa0c7f-60ee-4fa4-8b67-65e7ef10059a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_a9e2d067-fad9-43dd-a983-f32ce88a34c5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_a9e2d067-fad9-43dd-a983-f32ce88a34c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_baa540c6-638c-4058-8630-0e0b5739afc2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_baa540c6-638c-4058-8630-0e0b5739afc2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionConvertedInstrumentAmount1_60230890-3aac-4824-a677-d78c0167daa1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtConversionConvertedInstrumentAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtConversionConvertedInstrumentAmount1_60230890-3aac-4824-a677-d78c0167daa1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_2e5368df-8ccb-465a-8f93-cafdcc32903e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_2e5368df-8ccb-465a-8f93-cafdcc32903e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_6b190b62-27eb-4eaa-8028-fde7b8dcf55e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_6b190b62-27eb-4eaa-8028-fde7b8dcf55e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_edeb0e66-7f23-49ec-ada1-b1b9d70f2942" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_edeb0e66-7f23-49ec-ada1-b1b9d70f2942" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_638fe0e6-4498-49c6-9a2f-e41724595878" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_638fe0e6-4498-49c6-9a2f-e41724595878" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesIssued1_9c723f67-ea64-4b3e-bd9b-4ec4fdb65e21" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesIssued1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_NotesIssued1_9c723f67-ea64-4b3e-bd9b-4ec4fdb65e21" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent_04be227c-7503-4d9e-a682-9976b46d73ff" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent_04be227c-7503-4d9e-a682-9976b46d73ff" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebt_78bd62f6-362c-4a2b-a72d-af939149bc23" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_ConvertibleDebt_78bd62f6-362c-4a2b-a72d-af939149bc23" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_2c49be71-c1d7-4644-8af0-2f4566adaa2d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_2c49be71-c1d7-4644-8af0-2f4566adaa2d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_ae517e23-a46c-4a81-85df-c25fc1328cb5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_ae517e23-a46c-4a81-85df-c25fc1328cb5" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtCurrent_8d7521a9-7d67-40c0-a3c2-299491bfe462" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_ConvertibleDebtCurrent_8d7521a9-7d67-40c0-a3c2-299491bfe462" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_ec1c0b29-4c3b-43f5-989e-cfa28bbc6770" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_ec1c0b29-4c3b-43f5-989e-cfa28bbc6770" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_356dbb3b-4964-45b7-9ad9-a8616714583e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2ec12d7e-9002-475b-be69-5e54ffec39cd" xlink:to="loc_us-gaap_DebtInstrumentTable_356dbb3b-4964-45b7-9ad9-a8616714583e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtAxis_d6cfc230-2535-492d-98ba-3a2f4ffe74b9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ExtinguishmentOfDebtAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_356dbb3b-4964-45b7-9ad9-a8616714583e" xlink:to="loc_us-gaap_ExtinguishmentOfDebtAxis_d6cfc230-2535-492d-98ba-3a2f4ffe74b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_d6cfc230-2535-492d-98ba-3a2f4ffe74b9_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ExtinguishmentOfDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ExtinguishmentOfDebtAxis_d6cfc230-2535-492d-98ba-3a2f4ffe74b9" xlink:to="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_d6cfc230-2535-492d-98ba-3a2f4ffe74b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_56788767-d1f7-4ea9-a1fe-18df776d3162" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ExtinguishmentOfDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ExtinguishmentOfDebtAxis_d6cfc230-2535-492d-98ba-3a2f4ffe74b9" xlink:to="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_56788767-d1f7-4ea9-a1fe-18df776d3162" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_86957339-ac7c-41f1-98a3-ff9bfa731c91" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_56788767-d1f7-4ea9-a1fe-18df776d3162" xlink:to="loc_us-gaap_ConvertibleDebtMember_86957339-ac7c-41f1-98a3-ff9bfa731c91" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_57527337-a926-49ea-b232-76d148164825" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_356dbb3b-4964-45b7-9ad9-a8616714583e" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_57527337-a926-49ea-b232-76d148164825" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_57527337-a926-49ea-b232-76d148164825_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_57527337-a926-49ea-b232-76d148164825" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_57527337-a926-49ea-b232-76d148164825_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_992db68a-cdc6-49b7-9856-299915229184" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_57527337-a926-49ea-b232-76d148164825" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_992db68a-cdc6-49b7-9856-299915229184" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_d62a33e1-444b-4b49-8609-ba7a3e515312" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_992db68a-cdc6-49b7-9856-299915229184" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_d62a33e1-444b-4b49-8609-ba7a3e515312" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_71b7d197-8069-4786-9dc9-1a44eeb687a4" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_356dbb3b-4964-45b7-9ad9-a8616714583e" xlink:to="loc_srt_RangeAxis_71b7d197-8069-4786-9dc9-1a44eeb687a4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_71b7d197-8069-4786-9dc9-1a44eeb687a4_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_71b7d197-8069-4786-9dc9-1a44eeb687a4" xlink:to="loc_srt_RangeMember_71b7d197-8069-4786-9dc9-1a44eeb687a4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_6fe8d02b-d0ae-4f41-b613-d9d1f549f639" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_71b7d197-8069-4786-9dc9-1a44eeb687a4" xlink:to="loc_srt_RangeMember_6fe8d02b-d0ae-4f41-b613-d9d1f549f639" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_095d9044-4f54-48c3-83a4-df6992b7e271" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_6fe8d02b-d0ae-4f41-b613-d9d1f549f639" xlink:to="loc_srt_MaximumMember_095d9044-4f54-48c3-83a4-df6992b7e271" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_cd6ae547-1d0a-4835-8a4b-50c5e50c8cb1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_356dbb3b-4964-45b7-9ad9-a8616714583e" xlink:to="loc_us-gaap_DebtInstrumentAxis_cd6ae547-1d0a-4835-8a4b-50c5e50c8cb1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_cd6ae547-1d0a-4835-8a4b-50c5e50c8cb1_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_cd6ae547-1d0a-4835-8a4b-50c5e50c8cb1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_cd6ae547-1d0a-4835-8a4b-50c5e50c8cb1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7f766a7e-95b9-4ee6-a560-8046f23a63ee" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_cd6ae547-1d0a-4835-8a4b-50c5e50c8cb1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7f766a7e-95b9-4ee6-a560-8046f23a63ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2022Member_40e8df5b-e937-49d0-903f-4900da46ec96" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7f766a7e-95b9-4ee6-a560-8046f23a63ee" xlink:to="loc_hlit_ConvertibleNotedue2022Member_40e8df5b-e937-49d0-903f-4900da46ec96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2024Member_5c925f80-ce87-4eec-8422-3a3c4731ee34" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7f766a7e-95b9-4ee6-a560-8046f23a63ee" xlink:to="loc_hlit_ConvertibleNotedue2024Member_5c925f80-ce87-4eec-8422-3a3c4731ee34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionByUniqueDescriptionAxis_d1a400dd-bd49-4c5a-94b9-af136510b75f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtConversionByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_356dbb3b-4964-45b7-9ad9-a8616714583e" xlink:to="loc_us-gaap_DebtConversionByUniqueDescriptionAxis_d1a400dd-bd49-4c5a-94b9-af136510b75f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionNameDomain_d1a400dd-bd49-4c5a-94b9-af136510b75f_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtConversionNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtConversionByUniqueDescriptionAxis_d1a400dd-bd49-4c5a-94b9-af136510b75f" xlink:to="loc_us-gaap_DebtConversionNameDomain_d1a400dd-bd49-4c5a-94b9-af136510b75f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionNameDomain_41cb4e46-f1c3-41dc-bce8-7681125943a4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtConversionNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtConversionByUniqueDescriptionAxis_d1a400dd-bd49-4c5a-94b9-af136510b75f" xlink:to="loc_us-gaap_DebtConversionNameDomain_41cb4e46-f1c3-41dc-bce8-7681125943a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_Stockpricegreaterorequal130percentofNoteConversionPriceMember_17b22479-a0a6-40d4-a924-199b1d9c07a5" xlink:href="hlit-20210402.xsd#hlit_Stockpricegreaterorequal130percentofNoteConversionPriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtConversionNameDomain_41cb4e46-f1c3-41dc-bce8-7681125943a4" xlink:to="loc_hlit_Stockpricegreaterorequal130percentofNoteConversionPriceMember_17b22479-a0a6-40d4-a924-199b1d9c07a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_Notepricelessthan98percentofstockpricetimesconversionrateMember_e9135ccb-04c9-41ff-8fdd-1c36a35da42a" xlink:href="hlit-20210402.xsd#hlit_Notepricelessthan98percentofstockpricetimesconversionrateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtConversionNameDomain_41cb4e46-f1c3-41dc-bce8-7681125943a4" xlink:to="loc_hlit_Notepricelessthan98percentofstockpricetimesconversionrateMember_e9135ccb-04c9-41ff-8fdd-1c36a35da42a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ConvertibleDebtConvertibleNotesRollForwardDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#ConvertibleDebtConvertibleNotesRollForwardDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ConvertibleDebtConvertibleNotesRollForwardDetails" xlink:type="extended" id="id0d2440b97414200ae031e260b6a5795_ConvertibleDebtConvertibleNotesRollForwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_2de52b09-b4c7-4c04-a9c8-da5824d4a535" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_20af93d2-4a83-49bc-afc0-ecf4642a4794" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2de52b09-b4c7-4c04-a9c8-da5824d4a535" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_20af93d2-4a83-49bc-afc0-ecf4642a4794" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_6874557f-d9c1-4cfd-8829-868ebdd75be5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2de52b09-b4c7-4c04-a9c8-da5824d4a535" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_6874557f-d9c1-4cfd-8829-868ebdd75be5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_271c694d-8eca-4edc-bc1a-9781ee2b166d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2de52b09-b4c7-4c04-a9c8-da5824d4a535" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_271c694d-8eca-4edc-bc1a-9781ee2b166d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtNoncurrent_4b88f0f0-77ba-4f6a-90f2-852080a36956" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2de52b09-b4c7-4c04-a9c8-da5824d4a535" xlink:to="loc_us-gaap_ConvertibleDebtNoncurrent_4b88f0f0-77ba-4f6a-90f2-852080a36956" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleRemainingDiscountAmortizationPeriod1_0a36e223-954b-4441-b1a5-991c236a5116" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleRemainingDiscountAmortizationPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2de52b09-b4c7-4c04-a9c8-da5824d4a535" xlink:to="loc_us-gaap_DebtInstrumentConvertibleRemainingDiscountAmortizationPeriod1_0a36e223-954b-4441-b1a5-991c236a5116" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_5a913a43-705f-4475-9a66-184c0da63625" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2de52b09-b4c7-4c04-a9c8-da5824d4a535" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_5a913a43-705f-4475-9a66-184c0da63625" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_f77c0812-f5e8-4d14-b8f2-6d84a8f1b347" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2de52b09-b4c7-4c04-a9c8-da5824d4a535" xlink:to="loc_us-gaap_DebtInstrumentTable_f77c0812-f5e8-4d14-b8f2-6d84a8f1b347" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_f3fbf2c2-a404-4463-9bca-33bcdc649885" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_f77c0812-f5e8-4d14-b8f2-6d84a8f1b347" xlink:to="loc_us-gaap_DebtInstrumentAxis_f3fbf2c2-a404-4463-9bca-33bcdc649885" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_f3fbf2c2-a404-4463-9bca-33bcdc649885_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_f3fbf2c2-a404-4463-9bca-33bcdc649885" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_f3fbf2c2-a404-4463-9bca-33bcdc649885_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_94ba1958-99e3-4d70-8c3a-7b558915b900" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_f3fbf2c2-a404-4463-9bca-33bcdc649885" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_94ba1958-99e3-4d70-8c3a-7b558915b900" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2022Member_b906ab32-9300-47d3-8e66-786169b114e2" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_94ba1958-99e3-4d70-8c3a-7b558915b900" xlink:to="loc_hlit_ConvertibleNotedue2022Member_b906ab32-9300-47d3-8e66-786169b114e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2024Member_a22893af-5f5c-4cfa-9ea7-5d6fa68c52e0" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_94ba1958-99e3-4d70-8c3a-7b558915b900" xlink:to="loc_hlit_ConvertibleNotedue2024Member_a22893af-5f5c-4cfa-9ea7-5d6fa68c52e0" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/ConvertibleDebtInterestDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#ConvertibleDebtInterestDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/ConvertibleDebtInterestDetails" xlink:type="extended" id="i102427568872492791ae81caddd92c49_ConvertibleDebtInterestDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_61a54d8c-b833-416a-9b57-5f17acd82f3e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebtExcludingAmortization_6389ace8-5ca5-408b-9bac-df874cad967c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpenseDebtExcludingAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_61a54d8c-b833-416a-9b57-5f17acd82f3e" xlink:to="loc_us-gaap_InterestExpenseDebtExcludingAmortization_6389ace8-5ca5-408b-9bac-df874cad967c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfDebtDiscountPremium_19713cc4-74a5-4a71-9b3a-1c8a7de8518c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AmortizationOfDebtDiscountPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_61a54d8c-b833-416a-9b57-5f17acd82f3e" xlink:to="loc_us-gaap_AmortizationOfDebtDiscountPremium_19713cc4-74a5-4a71-9b3a-1c8a7de8518c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_dcf029e6-3e95-418a-afea-895021170223" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_61a54d8c-b833-416a-9b57-5f17acd82f3e" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_dcf029e6-3e95-418a-afea-895021170223" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_5447b433-b1b0-46f8-9cbd-7c187631baff" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_61a54d8c-b833-416a-9b57-5f17acd82f3e" xlink:to="loc_us-gaap_InterestExpenseDebt_5447b433-b1b0-46f8-9cbd-7c187631baff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_a1c1b042-b0db-4a95-b20e-a5ac653bcb9d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_61a54d8c-b833-416a-9b57-5f17acd82f3e" xlink:to="loc_us-gaap_DebtInstrumentTable_a1c1b042-b0db-4a95-b20e-a5ac653bcb9d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_43b2e8cb-6464-4dab-a742-ddb3de98aabf" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a1c1b042-b0db-4a95-b20e-a5ac653bcb9d" xlink:to="loc_us-gaap_DebtInstrumentAxis_43b2e8cb-6464-4dab-a742-ddb3de98aabf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_43b2e8cb-6464-4dab-a742-ddb3de98aabf_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_43b2e8cb-6464-4dab-a742-ddb3de98aabf" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_43b2e8cb-6464-4dab-a742-ddb3de98aabf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_acf3db5d-bfda-4971-ac2b-78095e991c71" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_43b2e8cb-6464-4dab-a742-ddb3de98aabf" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_acf3db5d-bfda-4971-ac2b-78095e991c71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2022Member_a29e99a1-e1b4-468f-bedc-6e777de59579" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_acf3db5d-bfda-4971-ac2b-78095e991c71" xlink:to="loc_hlit_ConvertibleNotedue2022Member_a29e99a1-e1b4-468f-bedc-6e777de59579" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2024Member_532fbdb1-9ec6-4727-9f0e-da1ae121b0a5" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_acf3db5d-bfda-4971-ac2b-78095e991c71" xlink:to="loc_hlit_ConvertibleNotedue2024Member_532fbdb1-9ec6-4727-9f0e-da1ae121b0a5" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/FairValueMeasurements" xlink:type="simple" xlink:href="hlit-20210402.xsd#FairValueMeasurements"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/FairValueMeasurements" xlink:type="extended" id="ic1a8fccd5da942c8b1b501f6a7c16da3_FairValueMeasurements"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/FairValueMeasurementsTables" xlink:type="simple" xlink:href="hlit-20210402.xsd#FairValueMeasurementsTables"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/FairValueMeasurementsTables" xlink:type="extended" id="i2f8612cd30fa49c88b0a1f28c28fef08_FairValueMeasurementsTables"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/FairValueMeasurementsFinancialAssetsandLiabilitiesMeasuredatFairValueBasedonThreeTierFairValueHierarchyDetail" xlink:type="simple" xlink:href="hlit-20210402.xsd#FairValueMeasurementsFinancialAssetsandLiabilitiesMeasuredatFairValueBasedonThreeTierFairValueHierarchyDetail"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/FairValueMeasurementsFinancialAssetsandLiabilitiesMeasuredatFairValueBasedonThreeTierFairValueHierarchyDetail" xlink:type="extended" id="i0d185ca6d43d4143904c3ca991024bb3_FairValueMeasurementsFinancialAssetsandLiabilitiesMeasuredatFairValueBasedonThreeTierFairValueHierarchyDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_e963c8e8-ff08-43c4-b8b6-d1b649f8a1c2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtNoncurrent_8c03c63a-35ec-41db-b773-9a1dc52cfc03" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_e963c8e8-ff08-43c4-b8b6-d1b649f8a1c2" xlink:to="loc_us-gaap_ConvertibleDebtNoncurrent_8c03c63a-35ec-41db-b773-9a1dc52cfc03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtFairValueDisclosures_718146c1-7e49-432a-9d6e-a078aa278d91" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtFairValueDisclosures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_e963c8e8-ff08-43c4-b8b6-d1b649f8a1c2" xlink:to="loc_us-gaap_ConvertibleDebtFairValueDisclosures_718146c1-7e49-432a-9d6e-a078aa278d91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_1340593b-91ab-40b2-9a21-2ef639be970c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_e963c8e8-ff08-43c4-b8b6-d1b649f8a1c2" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_1340593b-91ab-40b2-9a21-2ef639be970c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_aeeea88e-9df1-4dc7-b254-8d1b78754581" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_1340593b-91ab-40b2-9a21-2ef639be970c" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_aeeea88e-9df1-4dc7-b254-8d1b78754581" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_aeeea88e-9df1-4dc7-b254-8d1b78754581_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_aeeea88e-9df1-4dc7-b254-8d1b78754581" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_aeeea88e-9df1-4dc7-b254-8d1b78754581_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_3aed3a00-e35d-4774-bb6f-4df507add980" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_aeeea88e-9df1-4dc7-b254-8d1b78754581" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_3aed3a00-e35d-4774-bb6f-4df507add980" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_7ad5daf3-3831-4092-8f73-64f8541b0326" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_3aed3a00-e35d-4774-bb6f-4df507add980" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_7ad5daf3-3831-4092-8f73-64f8541b0326" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_082b89fe-6746-4963-9a12-d4d98d1efa22" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_1340593b-91ab-40b2-9a21-2ef639be970c" xlink:to="loc_us-gaap_DebtInstrumentAxis_082b89fe-6746-4963-9a12-d4d98d1efa22" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_082b89fe-6746-4963-9a12-d4d98d1efa22_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_082b89fe-6746-4963-9a12-d4d98d1efa22" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_082b89fe-6746-4963-9a12-d4d98d1efa22_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_4076eeb5-3db6-4a80-ab8f-1491038010eb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_082b89fe-6746-4963-9a12-d4d98d1efa22" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_4076eeb5-3db6-4a80-ab8f-1491038010eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2024Member_3dde3d3b-e12b-40f8-b66f-581ae187c008" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_4076eeb5-3db6-4a80-ab8f-1491038010eb" xlink:to="loc_hlit_ConvertibleNotedue2024Member_3dde3d3b-e12b-40f8-b66f-581ae187c008" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_ConvertibleNotedue2022Member_cc53bb28-c12c-4dfa-99f8-c68a2d5cdf0b" xlink:href="hlit-20210402.xsd#hlit_ConvertibleNotedue2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_4076eeb5-3db6-4a80-ab8f-1491038010eb" xlink:to="loc_hlit_ConvertibleNotedue2022Member_cc53bb28-c12c-4dfa-99f8-c68a2d5cdf0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_3d3136ec-4563-4f11-9c55-40ef74ec201b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_1340593b-91ab-40b2-9a21-2ef639be970c" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_3d3136ec-4563-4f11-9c55-40ef74ec201b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_3d3136ec-4563-4f11-9c55-40ef74ec201b_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_3d3136ec-4563-4f11-9c55-40ef74ec201b" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_3d3136ec-4563-4f11-9c55-40ef74ec201b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_c27358fc-2a4b-4c4a-9cf2-7d087c173468" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_3d3136ec-4563-4f11-9c55-40ef74ec201b" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_c27358fc-2a4b-4c4a-9cf2-7d087c173468" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_72b11161-4e74-4191-8948-2d1990ab24a0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_c27358fc-2a4b-4c4a-9cf2-7d087c173468" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_72b11161-4e74-4191-8948-2d1990ab24a0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/EarningsPerShare" xlink:type="simple" xlink:href="hlit-20210402.xsd#EarningsPerShare"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/EarningsPerShare" xlink:type="extended" id="i21b333a18dad430797308d2fc481aed7_EarningsPerShare"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/EarningsPerShareTables" xlink:type="simple" xlink:href="hlit-20210402.xsd#EarningsPerShareTables"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/EarningsPerShareTables" xlink:type="extended" id="id9fd85fda4fe42b498d078c33e381f37_EarningsPerShareTables"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/EarningsPerShareAntidilutiveSecuritiesDetail" xlink:type="simple" xlink:href="hlit-20210402.xsd#EarningsPerShareAntidilutiveSecuritiesDetail"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/EarningsPerShareAntidilutiveSecuritiesDetail" xlink:type="extended" id="i112609dff5e344baa9ed7ab783ea8544_EarningsPerShareAntidilutiveSecuritiesDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e22b271b-4a58-4349-88f1-1bb0fad259c9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_f786b593-f8e6-46ca-b586-6a2e76ec6fb9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e22b271b-4a58-4349-88f1-1bb0fad259c9" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_f786b593-f8e6-46ca-b586-6a2e76ec6fb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_671b4c86-68b5-4dda-a1b3-584df6b1032f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e22b271b-4a58-4349-88f1-1bb0fad259c9" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_671b4c86-68b5-4dda-a1b3-584df6b1032f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_e59aadde-cdef-4b6b-8dac-e6635cc9f07d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_671b4c86-68b5-4dda-a1b3-584df6b1032f" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_e59aadde-cdef-4b6b-8dac-e6635cc9f07d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_e59aadde-cdef-4b6b-8dac-e6635cc9f07d_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_e59aadde-cdef-4b6b-8dac-e6635cc9f07d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_e59aadde-cdef-4b6b-8dac-e6635cc9f07d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_93e46f4c-bd5e-4da1-add5-b0649bdc45a7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_e59aadde-cdef-4b6b-8dac-e6635cc9f07d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_93e46f4c-bd5e-4da1-add5-b0649bdc45a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_725da526-1890-4841-aeca-1233e341d2b4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_93e46f4c-bd5e-4da1-add5-b0649bdc45a7" xlink:to="loc_us-gaap_ConvertibleDebtMember_725da526-1890-4841-aeca-1233e341d2b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_04b52ad8-7229-4ef1-8c6a-2d634a747e1b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_93e46f4c-bd5e-4da1-add5-b0649bdc45a7" xlink:to="loc_us-gaap_EmployeeStockOptionMember_04b52ad8-7229-4ef1-8c6a-2d634a747e1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_03a2393c-48ee-41b3-8a41-706ebd43dd0d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_93e46f4c-bd5e-4da1-add5-b0649bdc45a7" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_03a2393c-48ee-41b3-8a41-706ebd43dd0d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_74b40ba5-ae82-41e6-ba14-3e0806cf4fbb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_93e46f4c-bd5e-4da1-add5-b0649bdc45a7" xlink:to="loc_us-gaap_EmployeeStockMember_74b40ba5-ae82-41e6-ba14-3e0806cf4fbb" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/EarningsPerShareNarrativesDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#EarningsPerShareNarrativesDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/EarningsPerShareNarrativesDetails" xlink:type="extended" id="ib46690f6737c432894ebdace99933ceb_EarningsPerShareNarrativesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e8530143-0c6e-430b-b476-64f636a5aa0d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities_7ed92682-d797-4cc0-b6ba-4ac6ca9376d7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e8530143-0c6e-430b-b476-64f636a5aa0d" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities_7ed92682-d797-4cc0-b6ba-4ac6ca9376d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_005d2b13-c72b-4e04-a925-7850da00ada4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e8530143-0c6e-430b-b476-64f636a5aa0d" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_005d2b13-c72b-4e04-a925-7850da00ada4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_c485ed24-9be3-4cde-8041-95c7b5a46884" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_005d2b13-c72b-4e04-a925-7850da00ada4" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_c485ed24-9be3-4cde-8041-95c7b5a46884" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_c485ed24-9be3-4cde-8041-95c7b5a46884_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_c485ed24-9be3-4cde-8041-95c7b5a46884" xlink:to="loc_us-gaap_TypeOfAdoptionMember_c485ed24-9be3-4cde-8041-95c7b5a46884_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_0d468d5e-8520-4bc3-a19f-8b533cd51a38" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_c485ed24-9be3-4cde-8041-95c7b5a46884" xlink:to="loc_us-gaap_TypeOfAdoptionMember_0d468d5e-8520-4bc3-a19f-8b533cd51a38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_AccountingStandardsUpdate202006MemberMember_a594320c-2773-470d-9e61-2aec3d4643e5" xlink:href="hlit-20210402.xsd#hlit_AccountingStandardsUpdate202006MemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_0d468d5e-8520-4bc3-a19f-8b533cd51a38" xlink:to="loc_hlit_AccountingStandardsUpdate202006MemberMember_a594320c-2773-470d-9e61-2aec3d4643e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_3af656af-d8c1-40ff-8ecc-be7f5dd03161" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_005d2b13-c72b-4e04-a925-7850da00ada4" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_3af656af-d8c1-40ff-8ecc-be7f5dd03161" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_3af656af-d8c1-40ff-8ecc-be7f5dd03161_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_3af656af-d8c1-40ff-8ecc-be7f5dd03161" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_3af656af-d8c1-40ff-8ecc-be7f5dd03161_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_99725eee-8e0c-4751-839a-d4c0995b208e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_3af656af-d8c1-40ff-8ecc-be7f5dd03161" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_99725eee-8e0c-4751-839a-d4c0995b208e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_1992b292-94a5-41ab-b540-a9a69622b91f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_99725eee-8e0c-4751-839a-d4c0995b208e" xlink:to="loc_us-gaap_SubsequentEventMember_1992b292-94a5-41ab-b540-a9a69622b91f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/SegmentInformation" xlink:type="simple" xlink:href="hlit-20210402.xsd#SegmentInformation"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/SegmentInformation" xlink:type="extended" id="i317690936ccf4cb8b5cb4bffc90d41f9_SegmentInformation"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/SegmentInformationTables" xlink:type="simple" xlink:href="hlit-20210402.xsd#SegmentInformationTables"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/SegmentInformationTables" xlink:type="extended" id="icc111293833c4ee1b077dfa76ab6215f_SegmentInformationTables"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/SegmentInformationSummaryFinancialInfomationbyreportablesegmentsDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#SegmentInformationSummaryFinancialInfomationbyreportablesegmentsDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/SegmentInformationSummaryFinancialInfomationbyreportablesegmentsDetails" xlink:type="extended" id="ic9cc7e2cbaf34e668d7955681a95c169_SegmentInformationSummaryFinancialInfomationbyreportablesegmentsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_e0f70320-1091-4b92-9a5d-b1fbd90a4452" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f62264df-11d0-4b90-ae50-f9508c1735c4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0f70320-1091-4b92-9a5d-b1fbd90a4452" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f62264df-11d0-4b90-ae50-f9508c1735c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_55b9d8dd-6f40-4928-b33c-f3d1a4242eb0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0f70320-1091-4b92-9a5d-b1fbd90a4452" xlink:to="loc_us-gaap_GrossProfit_55b9d8dd-6f40-4928-b33c-f3d1a4242eb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_ebd9ac00-3cfa-46e8-9395-47b02c511b78" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0f70320-1091-4b92-9a5d-b1fbd90a4452" xlink:to="loc_us-gaap_OperatingIncomeLoss_ebd9ac00-3cfa-46e8-9395-47b02c511b78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_82a88541-1fc5-4731-bcc6-ce2e5cb1aeec" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0f70320-1091-4b92-9a5d-b1fbd90a4452" xlink:to="loc_us-gaap_NumberOfReportableSegments_82a88541-1fc5-4731-bcc6-ce2e5cb1aeec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_24b45925-8147-4786-8e07-4328596627ff" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0f70320-1091-4b92-9a5d-b1fbd90a4452" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_24b45925-8147-4786-8e07-4328596627ff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_f94f374f-5db0-41c3-9c31-032e697b2586" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_24b45925-8147-4786-8e07-4328596627ff" xlink:to="loc_srt_ConsolidationItemsAxis_f94f374f-5db0-41c3-9c31-032e697b2586" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_f94f374f-5db0-41c3-9c31-032e697b2586_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_f94f374f-5db0-41c3-9c31-032e697b2586" xlink:to="loc_srt_ConsolidationItemsDomain_f94f374f-5db0-41c3-9c31-032e697b2586_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_c6caa77f-82ce-494c-a247-e4f558586e85" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_f94f374f-5db0-41c3-9c31-032e697b2586" xlink:to="loc_srt_ConsolidationItemsDomain_c6caa77f-82ce-494c-a247-e4f558586e85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_ca952851-dcf7-4cc5-9833-6daf0049e878" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_c6caa77f-82ce-494c-a247-e4f558586e85" xlink:to="loc_us-gaap_OperatingSegmentsMember_ca952851-dcf7-4cc5-9833-6daf0049e878" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_3ad59a83-e048-4018-af87-4fdf974ce4e2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_24b45925-8147-4786-8e07-4328596627ff" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_3ad59a83-e048-4018-af87-4fdf974ce4e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_3ad59a83-e048-4018-af87-4fdf974ce4e2_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_3ad59a83-e048-4018-af87-4fdf974ce4e2" xlink:to="loc_us-gaap_SegmentDomain_3ad59a83-e048-4018-af87-4fdf974ce4e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_040de9e7-f8bf-4255-a1cf-4acd15c2ff97" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_3ad59a83-e048-4018-af87-4fdf974ce4e2" xlink:to="loc_us-gaap_SegmentDomain_040de9e7-f8bf-4255-a1cf-4acd15c2ff97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_VideoMember_8abd7e27-cab2-44dc-b62c-322db6c10333" xlink:href="hlit-20210402.xsd#hlit_VideoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_040de9e7-f8bf-4255-a1cf-4acd15c2ff97" xlink:to="loc_hlit_VideoMember_8abd7e27-cab2-44dc-b62c-322db6c10333" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_CableAccessMember_8171d0ce-2061-44f4-9163-67be1533e9a3" xlink:href="hlit-20210402.xsd#hlit_CableAccessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_040de9e7-f8bf-4255-a1cf-4acd15c2ff97" xlink:to="loc_hlit_CableAccessMember_8171d0ce-2061-44f4-9163-67be1533e9a3" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/SegmentInformationSegmentIncomeorLossReconciliationDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#SegmentInformationSegmentIncomeorLossReconciliationDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/SegmentInformationSegmentIncomeorLossReconciliationDetails" xlink:type="extended" id="i3e538611efb64ef5acfca9be65af8cf2_SegmentInformationSegmentIncomeorLossReconciliationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_3ab3bd33-b724-4dd5-b4ee-69a9a3b24516" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_e7b535b9-31b2-43e5-8251-7aa812af68a6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3ab3bd33-b724-4dd5-b4ee-69a9a3b24516" xlink:to="loc_us-gaap_OperatingIncomeLoss_e7b535b9-31b2-43e5-8251-7aa812af68a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_39184e7e-e580-4306-875a-c70134929839" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3ab3bd33-b724-4dd5-b4ee-69a9a3b24516" xlink:to="loc_us-gaap_OperatingExpenses_39184e7e-e580-4306-875a-c70134929839" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_13073f94-9a93-4341-bb74-854e9b3f0a9c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3ab3bd33-b724-4dd5-b4ee-69a9a3b24516" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_13073f94-9a93-4341-bb74-854e9b3f0a9c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_5b775a3c-fa0b-4fe8-8637-0a61f10b878f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3ab3bd33-b724-4dd5-b4ee-69a9a3b24516" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_5b775a3c-fa0b-4fe8-8637-0a61f10b878f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_16a26b7f-9413-4511-842e-57785f3d2313" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3ab3bd33-b724-4dd5-b4ee-69a9a3b24516" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_16a26b7f-9413-4511-842e-57785f3d2313" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_1314c1e5-329e-4729-8201-cb5ea4fcb64c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3ab3bd33-b724-4dd5-b4ee-69a9a3b24516" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_1314c1e5-329e-4729-8201-cb5ea4fcb64c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_922f5c31-154d-4846-b9c8-91f964037cff" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_3ab3bd33-b724-4dd5-b4ee-69a9a3b24516" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_922f5c31-154d-4846-b9c8-91f964037cff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_de72e972-2539-4fae-be6a-e2d9bf3c88c9" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_922f5c31-154d-4846-b9c8-91f964037cff" xlink:to="loc_srt_ConsolidationItemsAxis_de72e972-2539-4fae-be6a-e2d9bf3c88c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_de72e972-2539-4fae-be6a-e2d9bf3c88c9_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_de72e972-2539-4fae-be6a-e2d9bf3c88c9" xlink:to="loc_srt_ConsolidationItemsDomain_de72e972-2539-4fae-be6a-e2d9bf3c88c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01c56978-ab93-4037-a373-56ac80a832c5" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_de72e972-2539-4fae-be6a-e2d9bf3c88c9" xlink:to="loc_srt_ConsolidationItemsDomain_01c56978-ab93-4037-a373-56ac80a832c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_2e3d45bc-3730-4f7d-9196-10badb2eac1a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01c56978-ab93-4037-a373-56ac80a832c5" xlink:to="loc_us-gaap_OperatingSegmentsMember_2e3d45bc-3730-4f7d-9196-10badb2eac1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_ba7676d4-d12c-4273-8067-ddd62ce7085a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01c56978-ab93-4037-a373-56ac80a832c5" xlink:to="loc_us-gaap_CorporateNonSegmentMember_ba7676d4-d12c-4273-8067-ddd62ce7085a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/SegmentGeographicInformationDetails" xlink:type="simple" xlink:href="hlit-20210402.xsd#SegmentGeographicInformationDetails"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/SegmentGeographicInformationDetails" xlink:type="extended" id="idacbc081dda741a991bb4e9a9a9074fe_SegmentGeographicInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_d315647f-e614-4e52-ba75-5946c1f86221" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a7b6602d-2c66-48f8-8231-a8e501827e30" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_d315647f-e614-4e52-ba75-5946c1f86221" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a7b6602d-2c66-48f8-8231-a8e501827e30" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_d5292c8b-89ed-47bf-8d46-9e43a035d79b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_d315647f-e614-4e52-ba75-5946c1f86221" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_d5292c8b-89ed-47bf-8d46-9e43a035d79b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_7f3e902f-6bda-420c-a049-eb30d87ab96e" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_d5292c8b-89ed-47bf-8d46-9e43a035d79b" xlink:to="loc_srt_StatementGeographicalAxis_7f3e902f-6bda-420c-a049-eb30d87ab96e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_7f3e902f-6bda-420c-a049-eb30d87ab96e_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_7f3e902f-6bda-420c-a049-eb30d87ab96e" xlink:to="loc_srt_SegmentGeographicalDomain_7f3e902f-6bda-420c-a049-eb30d87ab96e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_2c3d9c4a-dedc-4c06-ae1e-18593912decb" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_7f3e902f-6bda-420c-a049-eb30d87ab96e" xlink:to="loc_srt_SegmentGeographicalDomain_2c3d9c4a-dedc-4c06-ae1e-18593912decb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_0321056a-ceb9-4f8c-809d-f8b96702a02b" xlink:href="https://xbrl.sec.gov/country/2020/country-2020-01-31.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_2c3d9c4a-dedc-4c06-ae1e-18593912decb" xlink:to="loc_country_US_0321056a-ceb9-4f8c-809d-f8b96702a02b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_hlit_InternationalMember_99c0cd5e-93ad-4efb-b1b9-026f148e16f3" xlink:href="hlit-20210402.xsd#hlit_InternationalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_2c3d9c4a-dedc-4c06-ae1e-18593912decb" xlink:to="loc_hlit_InternationalMember_99c0cd5e-93ad-4efb-b1b9-026f148e16f3" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/CommitmentsandContingencies" xlink:type="simple" xlink:href="hlit-20210402.xsd#CommitmentsandContingencies"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/CommitmentsandContingencies" xlink:type="extended" id="i5c85725a8f55491eb6a5894c8dd40703_CommitmentsandContingencies"/>
  <link:roleRef roleURI="http://www.harmonicinc.com/role/CommitmentsandContingenciesAdditionalInformationDetail" xlink:type="simple" xlink:href="hlit-20210402.xsd#CommitmentsandContingenciesAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.harmonicinc.com/role/CommitmentsandContingenciesAdditionalInformationDetail" xlink:type="extended" id="if1d4436be02644ce838f02fb9ca0ea6e_CommitmentsandContingenciesAdditionalInformationDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_fc6b19cc-6dee-4c08-93d7-6d7b74f1068f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualAtCarryingValue_edd8a84a-45fa-434b-a644-4493551c189a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingencyAccrualAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_fc6b19cc-6dee-4c08-93d7-6d7b74f1068f" xlink:to="loc_us-gaap_LossContingencyAccrualAtCarryingValue_edd8a84a-45fa-434b-a644-4493551c189a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsTable_b66c5003-d7e6-4e0f-9fe4-1aad60c3501e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_fc6b19cc-6dee-4c08-93d7-6d7b74f1068f" xlink:to="loc_us-gaap_OtherCommitmentsTable_b66c5003-d7e6-4e0f-9fe4-1aad60c3501e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_b8088791-bdf6-43e3-8322-eacb548ed77d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_b66c5003-d7e6-4e0f-9fe4-1aad60c3501e" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_b8088791-bdf6-43e3-8322-eacb548ed77d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_b8088791-bdf6-43e3-8322-eacb548ed77d_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_b8088791-bdf6-43e3-8322-eacb548ed77d" xlink:to="loc_us-gaap_LossContingencyNatureDomain_b8088791-bdf6-43e3-8322-eacb548ed77d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_a1bb30f5-1926-4ad4-b1fc-e8a975aa5d12" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_b8088791-bdf6-43e3-8322-eacb548ed77d" xlink:to="loc_us-gaap_LossContingencyNatureDomain_a1bb30f5-1926-4ad4-b1fc-e8a975aa5d12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndemnificationGuaranteeMember_3559c73b-30e2-4909-b9cf-cae3c699c5c7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IndemnificationGuaranteeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_a1bb30f5-1926-4ad4-b1fc-e8a975aa5d12" xlink:to="loc_us-gaap_IndemnificationGuaranteeMember_3559c73b-30e2-4909-b9cf-cae3c699c5c7" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
