He was elected member of parliament for East Retford in 1689, before his accession to the peerage as 5th Earl of Kingston-upon-Hull on the death of his brother in 1690.[3][4] While serving as one of the commissioners for the union with Scotland, he was created Marquess of Dorchester in 1706, and took a leading part in the business of the House of Lords. He was made a privy councillor and in 1715 was created Duke of Kingston-upon-Hull; afterwards serving as Lord Privy Seal and Lord President of the Council. The Duke was a prominent figure in the fashionable society of his day.[5]
Family
His first wife was Lady Mary Feilding, a daughter of William Feilding, 3rd Earl of Denbigh, and his wife Mary King, whom he married in 1687. They had three daughters and a son:[6]
William Pierrepont, Earl of Kingston-upon-Hull, who died of smallpox, aged 20, in July 1713. He married Rachel, (legal daughter of Thomas Baynton of Little Chalfield, Wiltshire, but biological daughter and heiress of John Hall of Bradford, Wiltshire),[7][8] and had a daughter Frances (died 1795) and a son Evelyn.