Haig was born in Aldershot, Hampshire, the son of Francis W. and Shirley R. C. (née Brooks) Ward, an army officer, later Director of the Hayward Gallery, and opera singer, respectively, and educated at Rugby School. He lives in South London with his wife Julia who acts under the name Jane Galloway. They have five children. Haig and his wife are patrons of SANDS, a charity which deals with stillbirth and neonatal death. Haig was appointed Member of the Order of the British Empire (MBE) in the 2013 Birthday Honours for services to drama.