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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-04-16</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000737207</issuerCik>
        <issuerName>Marina Biotech, Inc.</issuerName>
        <issuerTradingSymbol>MRNA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001301582</rptOwnerCik>
            <rptOwnerName>Ranker Philip C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MARINA BIOTECH, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>17870 CASTLETON STREET, SUITE 250</rptOwnerStreet2>
            <rptOwnerCity>CITY OF INDUSTRY</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>91748</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Series E Convertible Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.50</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2018-04-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>18</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5000</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2018-04-16</value>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>180000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Warrants to Purchase Common Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.55</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2018-04-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>135000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2018-04-16</value>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>135000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>135000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">In connection with the closing of the issuer's private placement of shares of its Series E Convertible Preferred Stock and warrants to purchase shares of its common stock (the &quot;Offering&quot;), which occurred on April 16, 2018, the issuer and the reporting person agreed that the issuer would satisfy all accrued and unpaid fees owed by the issuer to the reporting person for services as a member of the issuer's Board of Directors prior to January 1, 2018 by the issuance by the issuer to the reporting person of 18 shares of Series E Preferred Stock and warrants to purchase 135,000 shares of common stock.</footnote>
        <footnote id="F2">Each outstanding share of Series E Preferred Stock shall be converted into common stock on the earliest to occur of: (i) any date more than 30 trading days after the closing of the Offering that the closing price of the common stock on each of the 30 days immediately prior to such conversion exceeds $5.00; (ii) the three year anniversary of the closing of the Offering; and (iii) the date on which the holders of a majority of the outstanding shares of Series E Preferred Stock elect to convert all of the outstanding shares of Series E Preferred Stock.</footnote>
        <footnote id="F3">The warrants expire on the five year anniversary of the closing of the Offering.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Philip C. Ranker</signatureName>
        <signatureDate>2018-04-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
