The siege of Fort Stanwix began on August 2, 1777 and ended on August 22, 1777. Fort Stanwix, at the western end of the Mohawk River Valley, was a primary defense point for the Continental Army against the British and indigenous forces aligned against them during the American Revolutionary War. The fort was occupied by Continental Army forces from New York and Massachusetts under the command of Colonel Peter Gansevoort. The besieging force was composed of British regulars, Loyalist soldiers, Hessians, and indigenous warriors, under the command of Brigadier General Barry St. Leger. St. Leger's expedition was a diversion in support of Lieutenant General John Burgoyne's campaign to take control of the Hudson River Valley to the east.

Barrimore Matthew "Barry" St. Leger was a British Army officer. St. Leger was active in the Saratoga Campaign, commanding an invasion force that unsuccessfully besieged Fort Stanwix. St. Leger remained on the frontier for the duration of the war; after its conclusion, he served briefly as commander of British forces in Quebec.