During the latter part of his service in the seven years’ war Campbell commanded H.M.S. Nightingale, based on Charleston, South Carolina, where he married a planter’s daughter, ‘esteemed one of the most considerable fortunes in the province’.
In 1773, through the influence of his brother, the Duke of Argyll, Lord William was transferred to the governorship of South Carolina. When he reached Carolina in June 1773 the provincial congress and its committees had virtually displaced royal government. Personally popular, he sought at first to placate the revolutionary leaders, many of whom were his wife’s connexions, but soon found the situation beyond his control. When the committee of safety, having obtained proof of Campbell’s negotiations for a rising of back country loyalists, considered a proposal ‘to take the governor into custody’, Campbell dissolved the assembly and secretly went aboard a man-of-war in Charleston harbour. After strong points commanding his anchorage had been captured by the rebels, Campbell set sail on 10 Jan. 1776 to join the expedition under Clinton, intended for the reduction of the Southern colonies. On the junction with Sir Peter Parker’s fleet, Campbell transferred to the flagship Bristol on which he served as a volunteer in the abortive attack on Charleston, and in the action at Sullivan’s Island on 28 June 1776 received ‘a contusion in his side’.
After joining Howe’s forces on Staten Island, New York, in August, Campbell left for England, arriving in December 1776. In March 1778 he was appointed to command a new ship, the Lion, but died at Southampton 4 Sept. 1778 of ‘a painful and lingering consumption which the physicians thought proceeded from the wounds he received on Sullivan’s island’.