He was the third and youngest son of James Campbell, 2nd Earl of Loudoun by his wife Margaret, daughter of Hugh Montgomerie, 7th Earl of Eglinton; Hugh Campbell, 3rd Earl of Loudoun was his elder brother. Campbell was married by contract dated 29 March 1720 to Jean, eldest daughter of David Boyle, 1st Earl of Glasgow by his second wife Jean, daughter and heiress of William Mure of Rowallan. They had two children: * James, born 11 February 1726, and * Margaret, born 17 May 1727.