Barclay was Secretary of State for Exiting the European Union from 2018 to 2020, Chief Secretary to the Treasury from 2020 to 2021, Minister for the Cabinet Office and Chancellor of the Duchy of Lancaster from 2021 to 2022, and Downing Street Chief of Staff from 5 February 2022 until 5 July 2022. He was the Secretary of State for Health and Social Care from 7 July 2022 until 6 September 2022. 