(a) Full name of discloser:

The Vanguard Group, Inc.

(b) Owner or controller of interests and short positions disclosed, if different from 1(a):

 The naming of nominee or vehicle companies is insufficient.  For a trust, the trustee(s), settlor and beneficiaries must be named.

(c) Name of offeror/offeree in relation to whose relevant securities this form relates:

 Use a separate form for each offeror/offeree

Horizon Therapeutics plc

(d) If an exempt fund manager connected with an offeror/offeree, state this and specify identity of offeror/offeree:

(e) Date position held/dealing undertaken:

 For an opening position disclosure, state the latest practicable date prior to the disclosure

04 January 2023

(f) In addition to the company in 1(c) above, is the discloser making disclosures in respect of any other party to the offer?

 If it is a cash offer or possible cash offer, state “N/A”

N/A

Class of relevant security:

(Note 3)

$0.0001 ordinary shares

Interests

Short positions

Number

%

Number

%

(1) Relevant securities owned and/or controlled:

21,243,953

9.37%

(2) Cash-settled derivatives:

(3) Stock-settled derivatives (including options) and agreements to purchase/sell:

 TOTAL:

21,243,953

9.37%

Class of relevant security

Purchase/sale

Number of securities

Price per unit

(Note 5)

$0.0001 ordinary shares

Sale

5,003

113.48 USD

$0.0001 ordinary shares

Purchase

10,500

113.48 USD

Class of relevant security

Product description

e.g. CFD

Nature of dealing

e.g. opening/closing a long/short position, increasing/reducing a long/short position

Number of reference securities

(Note 6)

Price per unit

(Note 5)

Not Applicable

Class of relevant security

Product description e.g. call option

Writing, purchasing, selling, varying etc.

Number of securities to which option relates

(Note 6)

Exercise price per unit

Type

e.g. American, European etc.

Expiry date

Option money paid/ received per unit

Not Applicable

Class of relevant security

Product description

e.g. call option

Exercising/ exercised against

Number of securities

Exercise price per unit

(Note 5)

Not Applicable

Class of relevant security

Nature of dealing

e.g. subscription, conversion

Details

Price per unit (if applicable)

(Note 5)

Not Applicable

Details of any indemnity or option arrangement, or any agreement or understanding, formal or informal, relating to relevant securities which may be an inducement to deal or refrain from dealing entered into by the person making the disclosure and any party to the offer or any person acting in concert with a party to the offer.

Irrevocable commitments and letters of intent should not be included. If there are no such agreements, arrangements or understandings, state “none”

Full details of any agreement, arrangement or understanding between the person disclosing and any other person relating to the voting rights of any relevant securities under any option referred to on this form or relating to the voting rights or future acquisition or disposal of any relevant securities to which any derivative referred to on this form is referenced. If none, this should be stated.

Is a Supplemental Form 8 (Open Positions) attached?

NO

Date of disclosure:

06 Ja