William Petty, 1st Marquess of Lansdowne

Shelburne served in the British Army and was an aide-de-camp to George III before becoming Member of Parliament for Wycombe in 1760. He succeeded to his father's peerages in 1761 before taking up his seat, and was elevated to the House of Lords, first sitting in 1764. He was appointed First Lord of Trade in 1763 but resigned a few months later, having failed to secure the inclusion of William Pitt in the Cabinet. In 1766 he was appointed Southern Secretary by Pitt but Pitt's illness meant that Shelburne's conciliatory approach to America was thwarted by his colleagues and the King. In 1768 he was dismissed from office and remained in opposition until 1782 when he joined Lord Rockingham's administration. He became Prime Minister on the sudden death of Rockingham and his appointment caused a number of the cabinet to resign in protest. His administration succeeded in negotiating terms of peace with the new United States before he was forced from office in 1783.