The sitter was the son of George Montague (d. 1739), 2nd Baron, who was created Earl of Halifax in 1715, and his second wife Mary, eldest daughter of Richard Lumley, 1st Earl of Scarsbrough (d. 1726). He greatly augmented the fortunes of his family by marrying, in 1741, Anne (d. 1753), only daughter of William Richards and heiress to Sir Thomas Dunk, a member of a wealthy family of clothiers from Kent, at which time he assumed the latter's family name. He pursued a successful political career rising to become Lord Lieutenant of Ireland in 1761-3, First Lord of the Admiralty in 1762, Lord Privy Seal in 1770 and Secretary of State in 1771. He was, however, perhaps most effective as head of the Board of Trade between 1748 and 1761 where he was responsible for greatly extending the commerce of the colonies and for which he earned the epithet 'The Founder of the Colonies'. The town of Halifax in Nova Scotia is named after him.