He was an Irish and English peer and member of the House of Lords (styled Hon.

He was also a Privy Counsellor, Chief Secretary for Ireland and Earl of Bessborough.

[3] On 2 June 1759 Ponsonby left the Treasury and was appointed Postmaster General of Great Britain jointly with Robert Hampden-Trevor, 1st Viscount Hampden.

He resigned the position when his brother-in-law, William Cavendish, 4th Duke of Devonshire, was dismissed as Lord Chamberlain in October 1762.

He was reappointed to the position (and sworn of the Privy Council) in July 1765 jointly with Thomas Robinson, 1st Baron Grantham, until he resigned in 1766, his initial offer to resign having been refused.