He was the eldest surviving son and heir of Hugh Fortescue, MP (1665–1719) of Filleigh, Weare Giffard and Ebrington, by his first wife Bridget Boscawen (d. 1708), daughter and sole heiress of Hugh Boscawen, MP (1625–1701), of Tregothnan in Cornwall (whose mother was a Rolle[1]), by his wife Lady Margaret Clinton (d. 1688), the youngest daughter and eventual co-heiress of Theophilus Clinton, 4th Earl of Lincoln, 12th Baron Clinton (1600–1667).
He also inherited Tattershall Castle in Lincolnshire, the Clinton seat, which was retained by the Fortescue family until 1910.
Having previously been a supporter of Prime Minister Walpole,[10] in 1733 he voted against his Excise Bill, which having faced substantial opposition failed to pass, and was dismissed from his royal posts as Gentleman of the Bedchamber to King George II and Lord Lieutenant of Devon,[11] as were also dismissed from their posts two dukes, four earls and two barons who had similarly defied Walpole.
[14] He consolidated his estates by selling most of his holdings in Somerset and Wiltshire and reinvesting the proceeds of £22,000 in purchasing more land in the vicinity of his North Devon manor of Filleigh, inherited from his father, where he demolished the ancient manor house and built in its place the surviving Palladian stately home which he named Castle Hill.
[15] He died unmarried on 3 May 1751,[16] aged 55, although he had fathered a daughter by a mistress, for whom he built a house on his Filleigh estate.