He was the eldest son of William Saint Quintin of Muston (1632–1695). He succeeded to the family baronetcy in November 1695 on the death of his grandfather, Sir Henry Saint Quintin of Harpham, who outlived his father by only a few days. His mother Elizabeth was the daughter of Sir William Strickland of Boynton, another local baronet.
Saint Quintin entered Parliament in 1695 as member for Kingston upon Hull, and served as the city"s Member of Parliament in eleven parliaments. A capable official, he held a series of responsible and lucrative posts: from 1698 to 1701 was a Commissioner of Customs, with the substantial salary of £1000 a year, but resigned the office when a new law barring the commissioners from sitting in Parliament came into force. From 1706 to 1713 he was a Commissioner of Revenue in Ireland, at the same salary, then from 1714 to 1717 a Lord of the Treasury.
In 1717 he became Commissioner of the Alienation Office, and in 1720 was appointed joint Vice-Treasurer, Receiver General and Paymaster of Ireland, offices he held until his death.
In the 1690s, he bought an estate at Scampston near Malton. Scampston Hall subsequently became the main family seat.
His body was interred at Saint John of Beverley Church Harpham.
1st Parliament of Great Britain. 2nd Parliament of Great Britain. 3rd Parliament of Great Britain.
4th Parliament of Great Britain.
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He was also a member of the Privy Council of Ireland.
