Harrowby was elected to his father's old Parliament seat of Tiverton in 1784. His administrative career began with an appointment to be Joint Parliamentary Under-Secretary of State for Foreign Affairs in 1789. In 1791 he was appointed joint Paymaster of the Forces, having been made Vice-President of the Board of Trade in 1790. He resigned the positions and also that of Treasurer of the Navy when he succeeded to his father's barony in June 1803. In 1804 he was Secretary of State for Foreign Affairs. After James Monroe's first interview with him on 30 May 1804, "...Monroe reported to his Government that Lord Harrowby's manners were designedly unfriendly; his reception was rough, his comments on the Senate's habit of mutilating treaties were harsh, his conduct throughout the intervuew was calculated to wound and to irritate."