Sec Form 4 Filing - THERO JOHN F @ AMARIN CORP PLC\UK - 2021-02-25

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person THERO JOHN F 2. Issuer Name and Ticker or Trading Symbol AMARIN CORP PLC\UK [ AMRN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) President and CEO (Last) (First) (Middle) C/O AMARIN PHARMA, INC., 440 US HIGHWAY 22 3. Date of Earliest Transaction (MM/DD/YY) 02/25/2021 (Street) BRIDGEWATER, NJ08807 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Ordinary Shares ( 1 ) 02/25/2021 M( 2 ) 390,696 A 3,272,445 D Ordinary Shares ( 1 ) 02/25/2021 F( 4 ) 153,739 D $ 7.3 3,118,706 D Ordinary Shares ( 1 ) 02/26/2021 M( 5 ) 6,736 A 3,125,442 D Ordinary Shares ( 1 ) 02/26/2021 M( 5 ) 6,736 A 3,132,178 D Ordinary Shares ( 1 ) 02/26/2021 M( 5 ) 13,472 A 3,145,650 D Ordinary Shares ( 1 ) 02/26/2021 F( 4 ) 10,604 D $ 6.74 3,135,046 D Ordinary Shares ( 1 ) 02/26/2021 M( 6 ) 59,367 A 3,194,413 D Ordinary Shares ( 1 ) 02/26/2021 F( 4 ) 23,361 D $ 6.74 3,171,052 ( 7 ) D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Restricted Stock Units ( 8 ) $ 0 02/25/2021 M 390,696 ( 2 ) ( 3 ) Ordinary Shares ( 1 ) 390,696 $ 0 94,304 D Restricted Stock Units ( 8 ) $ 0 02/26/2021 M 6,736 ( 5 ) ( 3 ) Ordinary Shares ( 1 ) 6,736 $ 0 40,416 D Restricted Stock Units ( 8 ) $ 0 02/26/2021 M 6,736 ( 5 ) ( 3 ) Ordinary Shares ( 1 ) 6,736 $ 0 40,416 D Restricted Stock Units ( 8 ) $ 0 02/26/2021 M 13,472 ( 5 ) ( 3 ) Ordinary Shares ( 1 ) 13,472 $ 0 80,832 D Restricted Stock Units ( 8 ) $ 0 02/26/2021 M 59,367 ( 6 ) ( 3 ) Ordinary Shares ( 1 ) 59,367 $ 0 118,733 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other THERO JOHN F C/O AMARIN PHARMA, INC. 440 US HIGHWAY 22 BRIDGEWATER, NJ08807 X President and CEO Signatures /s/ John F. Thero 03/01/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The Ordinary Shares may be represented by American Depositary Shares, each of which currently represents one Ordinary Share. ( 2 )As previously reported, on May 15 2017, the Reporting Person was granted 970,000 Restricted Stock Units ("RSUs") under the Amarin Corporation plc 2011 Stock Incentive Plan (the "Plan"). These RSUs consist of 3 tranches representing 25%, 25% and 50% of the total award. Each tranche vests ratably over 36 months beginning Sept. 30 2018 subject to achievement of certain prespecified performance criteria and continued service of the Reporting Person as provided in the RSU Award Agreement between the Issuer and Reporting Person. On Feb. 25 2021, pursuant to reporting of audited net total revenue for 2020 exceeding $500 million, the performance criteria related to the 50% tranche was deemed achieved, resulting in the vesting of 390,696 RSUs (29 of 36 months' worth). The remaining RSUs in this tranche will continue to vest over 7 monthly installments, the first of which vested Feb. 26 2021. The performance criteria related to both 25% tranches were previously deemed achieved (see Footnote 5). ( 3 )Not applicable. ( 4 )Represents withholding by the Issuer of shares in respect of tax liability incident to the vesting of a security issued in accordance with Rule 16b-3, and not a market sale of securities. ( 5 )As previously reported on February 27, 2020 and herewith in Footnote 2, on May 15, 2017, the Reporting Person was granted 970,000 RSUs under the Plan, of which the performance criteria related to two tranches representing 25% of the total award each was deemed achieved on February 25, 2020 pursuant to reporting of audited net product revenues for 2019 exceeding $400 million and of which the performance criteria related to one tranche representing 50% of the total award was deemed achieved on February 25, 2021 pursuant to reporting of audited net product revenues for 2020 exceeding $500 million. The tranches vest ratably over 36 months beginning September 30, 2018 subject to achievement of the performance criteria and continued service of the Reporting Person as provided in the RSU Award Agreement between the Issuer and Reporting Person. The thirtieth vesting event occurred on February 26, 2021. ( 6 )On March 2, 2020, the Reporting Person was granted 178,100 RSUs under the Plan. These RSUs vest in three equal installments on each of February 28, 2021, February 28, 2022 and February 28, 2023. The first vesting event occurred on February 26, 2021. ( 7 )Please see the section titled "Remarks" below for additional information. ( 8 )Each RSU represents a contingent right to receive one Ordinary Share or cash in lieu thereof at the Issuer's discretion.

Remarks: As of the date of this Form 4, the Reporting Person owns or holds the right to acquire an aggregate of 10,515,415 Ordinary Shares of the Issuer in the form of Ordinary Shares, stock options and RSUs outstanding under the Issuer's stock incentive plans, including but not limited to certain performance-based RSUs that are earned only if certain pre-defined operational milestones are achieved and, in certain cases, then vest only if the recipient remains with the company for an extended period of time.

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