Guy Carleton combined military service with the government of British Canada. He served in the Quebec campaign of 1759 and in later operations at Belle Île and Havana before becoming lieutenant governor of Quebec in 1766 and governor in 1768. His administration sought stability by working with French Canadian landholders and Catholic clergy rather than imposing rapid anglicization.

Carleton helped shape the Quebec Act of 1774, which protected Catholic religious practice and restored French civil law while retaining English criminal law. These concessions helped accommodate the conquered population but did not establish an elected assembly. During the American invasion of 1775, he defended Quebec against the forces of Richard Montgomery and Benedict Arnold. British reinforcements enabled the following year's counteroffensive, and his fleet defeated Arnold's flotilla on Lake Champlain at Valcour Island before winter ended further advance.

Returning as commander in chief in North America in 1782, Carleton supervised the British evacuation as the Revolutionary War ended. He resisted American demands to surrender Black people who had obtained freedom through British service or protection. Officials recorded evacuees in the Book of Negroes, providing documentation for departures from New York in 1783. Many went to Nova Scotia, where discrimination and hardship limited the security that evacuation had promised.

Created Baron Dorchester in 1786, he returned to British North America as governor in chief. Loyalist settlement, tensions between English and French legal traditions, and questions of representative government dominated this period. The Constitutional Act of 1791 divided Quebec into Upper and Lower Canada, a solution differing from some of his own preferences. He left Canada in 1796 and died in England in 1808. His career shaped British Canada's institutions amid conflicts between imperial security and competing local interests.