After the accession of George I, the Marquess of Dorchester (as he then was) was high in favour at Court, and honours were showered upon him with a lavish hand.

He was in 1714 appointed Lord Lieutenant of Wiltshire, and in the same year Chief Justice in Eyre, north of Trent, which latter dignity he held for two years.

In August, 1715, he was created Duke of Kingston upon Hull, in the county of Yorkshire.

He held the high office of Lord Privy Seal from 1716 to 1719 in the Administrations of Townshend and Stanhope, in the latter year becoming Lord President of the Council.
When Walpole became First Lord of the Treasury, the Duke again became Lord Privy Seal, and held the post until his death.

He was given the Garter in 1719, and was four times named as one of the Lord Justices of the Realm during the King's absences from England on visits to Hanover.
He had married, secondly, Isabella, fifth daughter of William Bentinck, first Earl of Portland, by his first wife, Anne, daughter of Sir Edward Villiers, who survived him two years.
The Duke had never really forgiven Lady Mary for eloping.