His father was William Dallas of North Newton (1719/20 – 2 October 1785), by his second wife, Davidona Haliburton (married 16 April 1754 at Old St. Paul's, Edinburgh). William Dallas, third son and heir to James Dallas of ST. MARTIN’S (baptised 16 June 1661 – 10 November 1740) by his second wife, Barbara Cockburn (married 1703 at Edinburgh), daughter of William Cockburn, merchant in Edinburgh, and his spouse Jean Clerk, and sister of Henrietta Cockburn, wife of William Dallas, W.S. of Budgate.