Sackville was born on 18 January 1688, the only son of Charles, 6th Earl of Dorset and his second wife Lady Mary Compton. He succeeded his father as 7th Earl of Dorset and 2nd Earl of Middlesex on 29 January 1708. In December that year he was appointed Constable of Dorset Castle and Lord Warden of the Cinque Ports. On the death of Queen Anne he was sent by the regency as Envoy-Extraordinary to Hanover to notify King George I. He carried the sceptre at the Coronation in 1714, and became First Lord of the Bedchamber; he was installed a Knight at the Garter the same year. In 1717 he left the King's service, he was created Duke of Dorset three years later. At the Coronation of King George II on 11 October 1727 he carried the Crown, and after resigning as Lord Steward of the Household, he was appointed Lord Lieutenant of Ireland. In this post he was a contraversial figure and in 1754 he was dismissed. He was Master of the Horse in 1755, holding the post for two years before taking up his original appointment as Constable of Dover Castle. He died at Knole on 9 October 1765.

In January 1709 he married Elizabeth, daughter of Lieut-General Walter Philip Colyear; they had three sons, the eldest of whom Charles succeeded as 2nd Duke, and three daughters.

This painting is after the full-length portrait at Knole (see J. Douglas Stewart, Sir Godfrey Kneller and the English Baroque Portrait, 1983, p.103, no.240, pl.69c)