<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-04-23</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001001902</issuerCik>
        <issuerName>INTEVAC INC</issuerName>
        <issuerTradingSymbol>IVAC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001325447</rptOwnerCik>
            <rptOwnerName>First Eagle Investment Management, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1345 AVENUE OF THE AMERICAS</rptOwnerStreet1>
            <rptOwnerStreet2>48TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10105</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001459708</rptOwnerCik>
            <rptOwnerName>21 APRIL FUND, LTD.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>CITCO FUND SERVICES (CAYMAN ISLANDS) LTD</rptOwnerStreet1>
            <rptOwnerStreet2>REGATTA OFFICE PARK WEST BAY ROAD</rptOwnerStreet2>
            <rptOwnerCity>GRAND CAYMAN</rptOwnerCity>
            <rptOwnerState>E9</rptOwnerState>
            <rptOwnerZipCode>KY1-1205</rptOwnerZipCode>
            <rptOwnerStateDescription>CAYMAN ISLANDS</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001637141</rptOwnerCik>
            <rptOwnerName>First Eagle Holdings, Inc.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1345 AVENUE OF THE AMERICAS</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10105</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2018-04-23</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>100003</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>6.0000</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4562058</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-04-23</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>121997</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>6.250</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4684055</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">This Form 4 is filed by 21 April Fund, Ltd. (&quot;April Ltd.&quot;), First Eagle Investment Management, LLC (&quot;FEIM&quot;) and First Eagle Holdings, Inc. (&quot;FEHI&quot; and, collectively with April Ltd. and FEIM, the &quot;Entities&quot;). The Entities disclaim status as a &quot;group&quot; for purposes of this Form 4.</footnote>
        <footnote id="F2">The shares of Common Stock reported herein are indirectly beneficially owned by FEHI and FEIM, a Delaware limited liability company and an investment adviser registered under the Investment Advisers Act of 1940. FEIM is (i) the registered investment adviser to April Ltd., (ii) a subsidiary of FEHI and (iii) investment adviser to certain separately managed accounts which, together with certain separate accounts managed by Michael M. Kellen in his individual capacity holding shares reported by FEIM for which FEIM disclaims beneficial ownership are defined herein as the &quot;Separately Managed Accounts&quot;. FEHI disclaims Section 16 beneficial ownership of the shares held directly by April Ltd. except to the extent, if any, of its pecuniary interest therein, and this report shall not be deemed an admission that FEHI is the Section 16 beneficial owner of any such securities.</footnote>
        <footnote id="F3">Represents 3,005,434 and 1,556,624 shares held directly by 21 April Ltd. and the Separately Managed Accounts, respectively. FEHI disclaims Section 16 beneficial ownership of the shares held directly by April Ltd. except to the extent, if any, of its pecuniary interest therein, and this report shall not be deemed an admission that FEHI is the Section 16 beneficial owner of any such securities.</footnote>
        <footnote id="F4">Represents 3,105,230 and 1,578,825 shares held directly by 21 April Ltd. and the Separately Managed Accounts, respectively. FEHI disclaims Section 16 beneficial ownership of the shares held directly by April Ltd. except to the extent, if any, of its pecuniary interest therein, and this report shall not be deemed an admission that FEHI is the Section 16 beneficial owner of any such securities.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>FIRST EAGLE INVESTMENT MANAGEMENT, LLC, By: /s/ Michael M. Kellen, Portfolio Manager</signatureName>
        <signatureDate>2018-04-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>FIRST EAGLE INVESTMENT MANAGEMENT, LLC, Investment Adviser of 21 April Fund, Ltd., By: /s/ Michael M. Kellen, Portfolio Manager</signatureName>
        <signatureDate>2018-04-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>FIRST EAGLE HOLDINGS, INC., By: /s/ Michael M. Kellen, Director</signatureName>
        <signatureDate>2018-04-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
