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U UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 25 , 2020 or TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Commission File Number : 001-35803 Ireland ( State or other jurisdiction of incorporation or organization ) Mallinckrodt plc ( Exact name of registrant as specified in its charter ) to College Business & Technology Park , Cruiserath , Blanchardstown , Dublin 15 , Ireland Accelerated Filer ( Address of principal executive offices ) ( Zip Code ) Telephone : +353 1 696 0000 ( Registrant's telephone number , including area code ) Securities registered pursuant to section 12 ( b ) of the Act : None Securities registered pursuant to Section 12 ( g ) of the Act : Title of each class Ordinary shares , par value $ 0.20 per share ( I.R.S. Employer Identification No. ) Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes No Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes No Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No 98-1088325 Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . 0 Non - accelerated Filer Large Accelerated Filer Smaller Reporting Company If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . ■ Emerging Growth Company Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Yes > No Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . Yes No > The aggregate market value of the voting and non - voting common equity held by non - affiliates of the Registrant ( assuming solely for the purposes of this calculation that all directors and executive officers of the Registrant are " affiliates " ) as of June 26 , 2020 , the last business day of the Registrant's most recently completed second fiscal quarter , was approximately $ 232.4 million ( based upon the closing price of $ 2.77 per share as reported by the New York Stock Exchange ( " NYSE " ) on that date ) . The number of shares of the registrant's common stock outstanding as of March 5 , 2021 was 84,505,217 . DOCUMENTS INCORPORATED BY REFERENCE Certain portions of the registrant's definitive proxy statement for its annual meeting of shareholders , to be filed with the Securities and Exchange Commission within 120 days after December 25 , 2020 , are incorporated by reference into Part III of this report .