(a) Full name of discloser:

Timothy P. Walbert

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

The naming of nominee or vehicle companies isinsufficient. For a trust, the trustee(s), settlor andbeneficiaries must be named.

N/A

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

Use a separate form for each offeror/offeree

Horizon Therapeutics plc

(d) Status of person making the disclosure:

e.g. offeror, offeree, person acting in concert with theofferor/offeree (specify name of offeror/offeree)

Person acting in concert with the offeree (namely, a director of the offeree)

(e) Date dealing undertaken:

January 3, 2023

(f) In addition to the company in 1(c) above, is thediscloser also making disclosures in respect ofany 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 2)

Ordinary shares of US$0.0001 each (" Ordinary Shares ")

Interests

Short positions

Number

%

Number

%

(1) Relevant securities ownedand/or controlled:

3,666,970

1.612%

-

-

(2) Cash-settled derivatives:

N/A

N/A

-

-

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

N/A

N/A

-

-

Total:

3,666,970

1.612%

-

-

Class of
relevant
security

Purchase/sale

Number of
securities

Price per unit
(Note 4)

N/A

N/A

N/A

N/A

Class of
relevant
security

Purchases/
sales

Total
number of
securities

Highest
price per
unit paid/
received

Lowest
price per
unit paid/
received

N/A

N/A

N/A

N/A

N/A

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 5)

Price
per unit
(Note 4)

N/A

N/A

N/A

N/A

N/A

Class of
relevant
security

Product
description
e.g. call
option

Writing,
purchasing,
selling,
varying etc.

Number
of
securities
to which
option
relates
(Note 5)

Exercise
price per
unit

Type
e.g.
American,
European
etc.

Expiry
date

Option
money
paid/
received
per unit

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

Class of
relevant
security

Product
description
e.g. call
option

Exercising/
exercised
against

Number of
securities

Exercise
price
per unit
(Note 4)

N/A

N/A

N/A

N/A

N/A

Class of
relevant
security

Nature of dealing
e.g. subscription,
conversion, exercise

Details

Price per unit
(if applicable)
(Note 4)

Ordinary Shares

Automatic vesting of performance stock units (“PSUs”) resulting in the issuance of new Ordinary Shares

Automatic vesting of 104,498 PSUs pursuant to the terms of the Horizon Therapeutics Public Limited Company Amended and Restated 2020 Equity Incentive Plan, which conferred on the discloser a right to receive 104,498 Ordinary Shares, of which 46,365 were withheld to cover taxes arising

$113.80

Details of any indemnity or option arrangement, or any agreementor understanding, formal or informal, relating to relevant securitieswhich may be an inducement to deal or refrain from dealingentered into by the party to the offer or person acting in concertmaking the disclosure and any other person:

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

N/A

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

N/A

Is a Supplemental Form 8 attached?

YES/NO

No

Date of disclosure:

January 4, 2023

Contact name:

Aidan Milstead

Telephone number:

+1 224 206 4983