UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

Mallinckrodt plc

(Name of Issuer)

Shares of Common Stock, par value $0.01 per share

(Title of Class of Securities)

G5890A102

(CUSIP Number)

John N. Spinney, Jr

Bracebridge Capital, LLC

888 Boylston Street, Suite 1500

Boston, MA 02199

(617) 497-3500

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

August 23, 2023

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. ☐

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Amendment No. 1 (the “Amendment”) amends and supplements the Schedule 13D filed by the Reporting Persons on June 16, 2023 (the “Original Schedule 13D”) and, as amended and supplemented by this Amendment, the “Schedule 13D”), with respect to the Shares. Capitalized terms used in this Amendment and not otherwise defined shall have the same meanings ascribed to them in the Original Schedule 13D.

Item 4 of the Original Schedule 13D is hereby amended and supplemented as follows:

On August 23, 2023, the Reporting Persons, along with creditors holding approximately 72% of the aggregate principal amount of the Debtors’ first lien funded debt and approximately 71% of the aggregate principal amount of the Debtors’ second lien funded debt and other parties thereto (collectively, the “Supporting Parties”), entered into a Restructuring Support Agreement (the “RSA”) with the Issuer and certain of its subsidiaries (together with the Issuer, the “Debtors”)

The RSA reflects an agreement by the Supporting Parties to support a comprehensive, reorganization of the Issuer and the other Debtors under chapter 11 of title 11 of the United States Code (the “Chapter 11 Cases”) with a prepackaged chapter 11 plan (the “Plan”), which contemplates the following:

The RSA also contemplates that Mallinckrodt will pursue an examinership proceeding in Ireland that would be consistent in all respects with the foregoing restructuring terms.

Pursuant to the RSA, the Reporting Persons as well as each of the Debtors and the Supporting Parties have made certain customary commitments to each other in connection with the pursuit of the transactions contemplated by the term sheets attached thereto. The RSA contains milestones for the progress of the Chapter 11 Cases in the Bankruptcy Court that the Issuer intends to initiate on or around August 28, 2023 (the “Milestones”), which include the dates by which the Debtors are required to, among other things, obtain certain orders of the Bankruptcy Court and consummate the Debtors’ emergence from bankruptcy. Among other dates set forth in the RSA, the RSA contemplates that the Bankruptcy Court shall have entered an order confirming the Plan no later than 50 days after the petition date of the Chapter 11 Cases and that the Debtors shall have emerged from bankruptcy no later than 90 days after the petition date.

Each of the parties to the RSA may terminate the RSA (and thereby their support for the Plan) under certain limited circumstances.

The transactions contemplated by the RSA are subject to approval by the Bankruptcy Court, among other conditions. Accordingly, no assurance can be given that the transactions described therein will be consummated.

The foregoing summary of the RSA does not purport to be complete and is qualified in its entirety by reference to the RSA, a copy of which is filed as Exhibit 99.2 hereto and incorporated herein by reference.

Bilateral Shareholder Agreements

In addition to the RSA, the Reporting Persons entered into a bilateral agreement with the Issuer (the “Bilateral Shareholder Agreement”). The Bilateral Shareholder Agreement generally obligates the Reporting Persons to support the restructuring in their capacities as shareholders. The foregoing summary of the Bilateral Shareholder Agreement does not purport to be complete and is qualified in its entirety by reference to the form of Bilateral Shareholder Agreement, a copy of which is filed as Exhibit 99.3 and incorporated herein by reference.

Item 7 of the Original Schedule 13D is hereby amended and supplemented as follows:

Signatures

After reasonable inquiry and to the best knowledge and belief of the undersigned, such person certifies that the information set forth in this Statement with respect to such person is true, complete and correct.

Date: August 24, 2023