Stephen Poyntz, born in London and baptised at St. Michael's, Cornhill in November 1685, was the second son of William Poyntz, upholsterer, of Cornhill, by his second wife, Jane, daughter of Stephen Monteage, merchant of London and Buckingham, whose wife was a sister of the regicide, Admiral Richard Deane. He was educated at Eton, being a King's Scholar and Captain of Montem in 1702. On 17th February 1703, he was admitted to King's College, Cambridge and, in due course, became a fellow, graduating as a BA in 1706 and MA five years later.

Shortly after he left college, Poyntz travelled with the Duke of Devonshire, and he also became tutor to the sons of Lord Townshend, with whom he was at the Hague in 1709 and 1710. For some time, he seems to have acted as Townshend's confidential secretary, communicating on his behalf with the English ambassadors abroad, and, through his employer's influence, he was introduced into the Diplomatic Service. In 1716, Poyntz was commissary to James, 1st Earl Stanhope, the Secretary of State, followed, in 1724, by the position of Envoy-Extraordinary and Plenipotentiary to Sweden. Of this latter mission Poyntz acquitted himself well, though Sir Robert Walpole complained of the large sums which he drew from the English exchequer to secure Sweden's support. In 1728, Poyntz was sent as commissioner to the congress at Soissons, where he made the acquaintance of George, 1st Baron Lyttelton, and he remained in France until the Summer of 1730.

On the formation of the household of the Duke of Cumberland, second son of King George II, in 1731, Poyntz was appointed as the young Duke's governor and steward of the household, and, throughout his life, he continued as the prince's trusted adviser. Although he had rooms in St. James' Palace, about 1735, Poyntz purchased, from the family of Hillersdon, an estate at Midgham, a chapelry in the parish of Thatcham, near Newbury in Berkshire. He became well known in the area and was always easily recognised by the red coat that he wore. The Duke of Cumberland spent some of his early years there and two rooms, long called 'the Duke's Rooms,' were added to the house for his accommodation. Ponytz became good friends with Queen Caroline (of Anspach) and, as a mark of esteem for his services, she placed a very beautiful vase, ornamented with figures in high relief, in the grounds at Midgham House.

Poyntz played an important part at the Royal Court. In 1734, he acted as the medium of communication between the King and Queen and an Austrian envoy. It was in his rooms at St. James's Palace that, in 1735, the famous Earl of Peterborough formally acknowledged to the company that Anastasia Robinson was his wife. In the same year, Poyntz was created a privy councillor and he received the sinecure post of inspector of prosecutions in the exchequer concerning 'prohibited and uncustomed goods.' He died at Midgham, on 17th December 1750, and was buried there. Horace Walpole says that he was "ruined in his circumstances by a devout brother, whom he had trusted, and by a simple wife, who had a devotion of marrying dozens of her poor cousins at his expense; you know she was the 'Fair Circassian.' Mr. Poyntz was called a very great man, but few knew anything of his talents, for he was timorous to childishness. The Duke has done greatly for his family and secured his places for his children, and sends his two sons abroad, allowing them £800 a year". Poyntz's influence at court, his talents, and his kindly disposition were acknowledged on all sides. Carlyle, in his 'Memoirs of Frederick the Great,' characteristically describes him as "once bright gentleman, now dim and obsolete."

Poyntz married, in February 1733, Anna Maria Mordaunt, daughter of the Hon. Brigadier-General Lewis Mordaunt and maid of honour to Queen Caroline. She had been a great beanty and her charms were described by Samuel Croxall in his poem of the 'Fair Circassian.' They had two sons - William of Midgham (d. 1809) and Charles, a prebendary at Durham Cathedral - and two daughters, Margaret Georgina and Louisa. The latter died unmarried, but Margaret Georgina became the wife, at Althorp on 27th December 1755, of John, afterwards 1st Earl Spencer. Mrs. Calderwood of Polton met the Spencers and the whole of the Poyntz family travelling through Spa in great state in 1756. Mrs. Poyntz was then a "deaf, short-sighted, loud-spoken, hackney-headed wife, and played at cards from morning till night." Mrs. Spencer was "a very sweet-like girl; her sister is a great hoyden." Mrs. Poyntz was in great favour at Versailles in August 1763, when she cured Madame Victoire of the stone. She died at Midgham, on 14th November 1771, and was buried in the parish church in Thatcham.

Poyntz was the author of a 'Vindication of the Barrier Treaty,' which has been erroneously printed among Bishop Hare's writings. It was an 'excellent work'. Lord Lyttelton, Lord Hervey, Sir C. Hanbury Williams, Nicholas Hardinge, and others addressed verses to Poyntz. He was also a friend of Samuel Richardson, the novelist. Through his agency, the sum of £100 is said to have been granted, by Queen Caroline, to Elizabeth Elstob, and when James Ferguson, the astronomer, came to London, in May 1743, be brought with him a letter of recommendation to Poyntz, who befriended him in every way. Ferguson drew the portraits of Mrs. Poyntz and the children, so that Poyntz might be able from personal knowledge to speak favourably of the skill of the artist.