Born in Carroll County, Maryland, Winchester enlisted in the Maryland militia during the American Revolution. He served Gen. Hugh Mercer's Flying Camp battalion during the early months of the war. He was captured by British forces during Gen. John Sullivan's failed attempt to take Staten Island on August 22, 1777. Winchester was released in a prisoner exchange, and in May 1778 he was commissioned a lieutenant in the 3rd Maryland Regiment. He was taken prisoner a second time at the surrender of Charlestown, South Carolina on May 12, 1780. Exchanged in December, he was promoted to captain and served the remainder of the war under Gen. Nathanael Greene.