Montgomery was born in Swords, County Dublin, Ireland, Great Britain to a wealthy family of Ulster Scots. Montgomery joined the British Army in 1756, and was transferred to the Thirteen Colonies, fighting in the French and Indian War. Afterwards, he returned to Britain for health reasons in 1761, and he joined the Templar Order secret society. In 1773, Montgomery returned to the Americas, where he settled down. Montgomery was commissioned as a Brigadier-General after becoming a member of the Continental Congress, as he was a man with military experience. Montgomery was given command of an army that would invade British Canada in the winter of 1775-1776, and his army captured Fort St. Jean (Montreal) from the British, capturing John Andre in the process. Montgomery would march on the Canadian capital of Quebec as another army also moved on the city, and on 31 December 1775 the American assault on Quebec began.