The siege of Fort St. Jean was conducted by American Brigadier General Richard Montgomery on the town and fort of Saint-Jean, also called St. John, St. Johns, or St. John's, in the British province of Quebec during the American Revolutionary War. The siege lasted from September 17 to November 3, 1775.

Richard Montgomery was an Irish-born American military officer who first served in the British Army. He later became a major general in the Continental Army during the American Revolutionary War, and he is most famous for leading the unsuccessful 1775 invasion of northeastern Quebec.