In Parliament, where he was member for Westminster from 1763 to 1776, he had opposed the policy that led to the American War of Independence. However, he was sent to Boston in 1774 with the local rank of brigadier general, colonel of the 5th Regiment of Foot (later called the Northumberland Fusiliers). His views on the military discipline were ahead of their time. "He detested corporal punishments. At a time when other commanders were resorting to floggings and firing squads on Boston Common, he led his regiment by precept and example." Politically a Whig, he at first sympathized with the colonials, but he soon began to despise their behavior. He led the relief column at the Battle of Lexington and Concord. Percy's intelligent actions probably saved the British forces from complete disaster that day.