His administrative career began with an appointment to be Joint Parliamentary Under-Secretary of State for Foreign Affairs in 1789.

[2] 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 interview was calculated to wound and to irritate.

"[3] In 1805 he was Chancellor of the Duchy of Lancaster under his intimate friend William Pitt; in the latter year he was sent on a special and important mission to the emperors of Austria and Russia and the king of Prussia as part of the Hanover Expedition.

Harrowby's long association with the Tories did not prevent him from assisting to remove the disabilities of Roman Catholics and Protestant dissenters, or from supporting the movement for electoral reform; he was also in favour of the emancipation of the slaves.

Lord Harrowby survived her by nine years and died in December 1847 at his Staffordshire residence, Sandon Hall, aged 85, being, as Charles Cavendish Fulke Greville says, "the last of his generation and of the colleagues of Mr Pitt, the sole survivor of those stirring times and mighty contests.