Carleton had been a soldier for 26 years and had seen action in the War of the Austrian Succession and the Seven Years War when he was appointed Governor of Quebec in 1768. When the North American Rebellion broke out, Carleton fought off an attempt by the rebels to conquer Quebec in 1775 - 76. Following the collapse of the Rebellion in 1778, Carleton was persuaded to remain Governor of Quebec. He traveled to London in 1780 to advise Lord North on the drafting of the Britannic Design, and it was at his suggestion that Quebec was added to the Confederation of North America as a separate confederation. Carleton was raised to the peerage, becoming 1st Baron Dorchester, at the same time John Burgoyne became 1st Duke of Albany. Dorchester was sworn in as first Governor-General of the Confederation of Quebec on July 2, 1782. Dorchester was able to work together with George Clinton, Governor of the Northern Confederation, to avert a border war between Quebec and the N.C. in 1788.
The city of Dorchester, Quebec is named after him.