 In 1771 he assumed by royal licence the surname and arms of Cornewall in lieu of his patronymic, in accordance with the bequest from his father-in-law, an inheritance which included Moccas Park in Herefordshire.In 1773 he received a Doctorate of Civil Law from the University of Oxford.Cornewall entered Parliament at the 1774 general election, as Member of Parliament for Herefordshire and held the seat until 1796.