X0306 4 2022-02-01 0 0001492426 Horizon Therapeutics Public Ltd Co HZNP 0001349376 Walbert Timothy P C/O HORIZON THERAPEUTICS PLC, 70 SAINT STEPHEN?S GREEN DUBLIN L2 D02 E2X4 IRELAND 1 1 0 0 Chairman, President and CEO Ordinary Shares 2022-02-01 4 M 0 9087 0.00 A 44690 I By spouse Ordinary Shares 2022-02-01 4 F 0 3767 94.33 D 40923 I By spouse Ordinary Shares 585549 D Ordinary Shares 107739 I See footnote Ordinary Shares 100300 I See footnote Restricted Stock Units (RSUs) 2022-02-01 4 M 0 9087 0.00 D Ordinary Shares 9087 0 I By spouse The shares are held by the Timothy P. Walbert 2021 Gift Trust, of which the Reporting Person's spouse is the Trustee and beneficiary. The shares are held by the Keli B. Walbert 2021 Gift Trust, of which the Reporting Person is the Trustee. The beneficiaries of the Trust include the Reporting Person and his descendants. Each RSU represents a contingent right to receive one ordinary share of the Issuer. The RSU's vest 1/3 annually on each anniversary of February 1, 2019 (the grant date). /s/ Miles W. McHugh, Attorney-in-Fact 2022-02-02