Augustus Henry FitzRoy, 3rd Duke of Grafton (28 September 1735 – 14 March 1811), styled Earl of Euston between 1747 and 1757, was a British Whig statesman of the Georgian era. He is one of a handful of dukes who have served as Prime Minister.
He became Prime Minister in 1768 at the age of 33, leading the supporters of William Pitt, and was the youngest person to have held the office until the appointment of William Pitt the Younger 15 years later. However, he struggled to demonstrate an ability to counter increasing challenges to Britain's global dominance following the nation's victory in the Seven Years' War. He was widely attacked for allowing France to annex Corsica, and stepped down in 1770, handing over power to Lord North.
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 3rd Duke of Grafton, which elevated him to the House of Lords.
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, he retired the following year, and Pitt (by then Lord Chatham) formed a ministry in which Grafton was First Lord of the Treasury but not Prime Minister.
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.