In 1756, he entered
Parliament as
MP for
Boroughbridge, a
pocket borough; several months later, he switched constituencies to
Bury St Edmunds, which was controlled by his family. However, a year later, his grandfather died, and he succeeded as the 3rd Duke of Grafton, which elevated him to the
House of Lords. Grafton was immediately created the
Lord Lieutenant of Suffolk and served in that capacity from 1757 to 1763, when he was dismissed by
Lord Bute. He would again serve in that position from 1769 to 1790. In November 1756, he was appointed
lord of the bedchamber to the
Prince of Wales but he resigned from the post in June 1758. He first became known in politics as an opponent of
Lord Bute, a favourite of
King George III. Grafton aligned himself with the
Duke of Newcastle against Lord Bute, whose term as prime minister was short-lived largely because it was felt that the peace terms to which he had agreed at the
Treaty of Paris were not a sufficient return for
Britain's performance in the Seven Years' War. In 1765, Grafton was appointed a
Privy Counsellor; then, following discussions with
William Pitt the Elder, he was appointed
Northern Secretary in
Lord Rockingham's first government. However, Rockingham retired the following year, and Pitt (by then Lord Chatham) formed a ministry in which Grafton was
First Lord of the Treasury but not the prime minister. The ministry that assumed office was composed of a diverse coalition, including supporters of the King, followers of Chatham, and members of the official
Whig faction. Initially, it maintained a fragile unity but was widely regarded as a temporary arrangement. Shortly after its formation, Chatham fell ill and withdrew to
Bath, ceasing to participate in government affairs or communicate with his colleagues. By March 1767, the direction of government had passed to Grafton, marking the end of Chatham's administration. On 20 September 1769, he was appointed a Knight of the
Order of the Garter.
Prime minister '' (1762) by
Pompeo Batoni. Grafton is shown in the uniform of a
West Suffolk Militia colonel. Chatham's illness, at the end of 1767, resulted in Grafton becoming the government's effective leader (he is credited with entering the office of prime minister in 1768), but political differences, the impact of the
Corsican Crisis and the attacks of "
Junius" led to his resignation in January 1770. Also, in 1768, Grafton became Chancellor of Cambridge University. He became
Lord Privy Seal in
Lord North's ministry (1771) but resigned in 1775, being in favour of conciliatory action towards the
American colonists. In the second Rockingham ministry of 1782, he was again Lord Privy Seal and continued in the post in the following
Shelburne ministry until March 1783. ==Militia career==