He was born in Ireland on September 3, 1724 and was commissioned into the British army as an ensign in the 25th Foot Regiment. By 1757 he had been promoted to the rank of Lieutenant Colonel in the 72nd foot and sailed up the St Lawrence with Wolfe in 1759. He fought in the Battle of the Plains of Abraham in September and was wounded. His friend and commander James Wolfe was killed in that same battle.

Like many high ranking military figures of the time, he was designated to be commissioned a Lieutenant Governor at one of the colonies in the British Empire, his being Quebec in 1766 and then in 1768 he was made Governor. He got to know the French Canadian society and leaders and became sympathique to their position. He helped with the passage of the Quebec Act in 1774 which benefited the seigniors and the Roman Catholic church in Quebec but held back the development of representative government. (See Quebec Act) He was also responsible for the preparation of the defence of Canada and the defeat of Montgomery and Arnold when they led the American forces against Quebec City in 1775-76. He did however have differences with the British Secretary of State for the Colonies, Lord George Germain and as a result, he  was recalled to England in 1778.

In 1782 as the American War of Independence was finally closing, he was asked to come out of retirement and take charge of al  of the forces in British North America in order to help British Loyalists and troops re-locate to Canada and in the case of the troops return to England. In particular he arranged for and oversaw the evacuation of New York City which had been a loyalist strong hold through the war.

Due to the impressive manner in which he carried out these duties, he was made Baron of Dorchester and appointed Governor in Chief of British North America. He served in this role until 1796 with one of the highlights being the passing of the second major piece of legislation during his term of office in the America's, the Constitutional Act of 1791. His guidance began the opening up of representative government in the colonies and helped maintain the Canada's  as a loyal, stable colony for Great Britain during a time of great conflict against the French and Napoleon.