William Pitt , 1st Earl of Chatham ( 15 November 1708 â `` 11 May 1778 ) was a prime minister of Great Britain . William Pitt , 1st Earl of Chatham PC ( 15 November 1708 -- 11 May 1778 ) was a British Whig statesman who achieved his greatest fame leading Britain during the Seven Years ' War ( known as the French and Indian War in North America ) .