 James Boswell acted as Campbell's legal advisor.Following his exciting electoral victory, Colonel Campbell left his elder brother, Sir James Campbell (1737–1805) of Killean, to keep his parliamentary seat warm and sailed for America in command of the 71st Regiment of Foot, Fraser's Highlanders, where the American Revolutionary War was in progress.In 1776, after a battle aboard a vessel in Boston Harbor, Campbell was captured by the Americans and held prisoner until 1778.