Stephen Poyntz (1685–1750) was an English diplomat and courtier.
Born in London, and baptised at St Michael Cornhill in November 1685, he was the second son of William Poyntz, upholsterer, of Cornhill, and his second wife, Jane, daughter of the merchant Stephen Monteage, whose wife was a sister of Richard Deane. He was educated at Eton College, a king's scholar and in 1702 captain of Montem. On 17 February 1703 he was admitted to King's College, Cambridge, and became in due course a Fellow there, graduating B.A. in 1706, and M.A. in 1711.
Shortly after he left college, Poyntz travelled with William Cavendish, 2nd Duke of Devonshire; and he was also tutor to the sons of Charles Townshend, 2nd Viscount Townshend, with whom he was at The Hague in 1709 and 1710. He acted as Townshend's confidential secretary, communicating on his behalf with the English ambassadors abroad, and, through his chief's influence, he moved into the diplomatic service. Poyntz was commissary in 1716 to James Stanhope, 1st Earl Stanhope, the Secretary of State.
Poyntz was made envoy-extraordinary and plenipotentiary to Sweden in July 1724. Sir Robert Walpole complained about sums he drew from the Exchequer to secure Sweden's support, but he managed to defend the reputation of Sir John Norris against accusations going back to the Great Northern War. In 1728 he was sent as commissioner to the Congress of Soissons, where he made the acquaintance of George Lyttelton, 1st Baron Lyttelton, and he remained in France until the summer of 1730. He obtained the French agreement to dismantle the fortifications at Dunkirk, regarded as a deft diplomatic coup as well as a political triumph for the Whigs in London.