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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-07-25</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001251769</issuerCik>
        <issuerName>Apollo Endosurgery, Inc.</issuerName>
        <issuerTradingSymbol>APEN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001373084</rptOwnerCik>
            <rptOwnerName>Crawford Matthew S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3600 N CAPITAL OF TEXAS HWY</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE B180</rptOwnerStreet2>
            <rptOwnerCity>AUSTIN</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>78746</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-07-25</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>45454</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.50</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>45454</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-07-25</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1090909</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.50</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1090909</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By PTV Evergreen Fund, LP.</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5243372</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">These securities are held in the name of PTV Evergreen Fund, LP. PTV Healthcare Capital has sole voting and investment control over the shares owned by PTV Evergreen Fund, LP. The Managing Directors of PTV Healthcare Capital have shared voting and investment control over the shares owned by PTV Evergreen Fund, LP. The Reporting Person is a Managing Partner of PTV Healthcare Capital and may be deemed to be the beneficial owner of the securities held by PTV Evergreen Fund, LP.</footnote>
        <footnote id="F2">Includes (i) 1,347,565 shares of common stock held by PTV IV, L.P., (ii) 605,712 shares of common stock held by PTV Special Opportunities I, L.P., (iii) 2,199,186 shares of common stock held by PTV Sciences II, L.P., and (iv) 1,090,909 shares held by PTV Evergreen Fund, LP. PTV Healthcare Capital has sole voting and investment control over the shares owned by PTV IV, L.P., PTV Special Opportunities I, L.P., PTV Sciences II, L.P., and PTV Evergreen Fund, LP. The Reporting Person is a Managing Partner of PTV Healthcare Capital and may be deemed to be the beneficial owner of the securities held by PTV IV, L.P., PTV Special Opportunities I, L.P., PTV Sciences II, L.P., and PTV Evergreen Fund, LP.</footnote>
    </footnotes>

    <remarks>Exhibit Index:  Exhibit 24 - Power of Attorney (incorporated by reference to the Power of Attorney filed as Exhibit 24 to the Form 3 filed by the Reporting Person on December 29, 2016)</remarks>

    <ownerSignature>
        <signatureName>/s/ Brian Szymczak - Attorney-in-Fact</signatureName>
        <signatureDate>2017-07-26</signatureDate>
    </ownerSignature>
</ownershipDocument>
