In September of that year he was elected member for the City of Westminster, on the death of Charles James Fox.

In 1807, he offered himself as a candidate for the county of Northumberland in opposition to Charles, Lord Howick (afterwards the 2nd Earl Grey), who declined to contest the seat.

He served as Ambassador Extraordinary at the coronation of Charles X of France in 1825, defraying the expenses thereof himself, and he "astonished the continental nobility of the magnitude of his retinue, the gorgeousness of his equippage, and the profuseness of his liberality".

He was thus in office when the Catholic Emancipation Act was passed, and was pronounced by Robert Peel "the best chief governor that ever presided over the affairs of Ireland.

He proposed the CBS's formation at a meeting in the Freemasons' Hall, London on 6 February 1818, chaired by the Archbishop of Canterbury.