Steephill Cottage, on the site of the present castle, near Ventnor, was built by him in 1770 at considerable expense, and he entertained there several foreign ambassadors (Hassell, Isle of Wight, i. 212–19; Guide to Southampton, 4th edit. p. 87).
In July 1766 Pitt made Stanley ambassador-extraordinary to Russia. He was instructed to proceed to St. Petersburg by way of Berlin, with credentials to the king of Prussia. The object of the mission was to make a ‘triple defensive alliance’ of Great Britain, Russia, and Prussia. The appointment was hastily made without the knowledge of Conway, then leading the House of Commons, without any intimation to Macartney, our ambassador at St. Petersburg, and without consultation with Sir Andrew Mitchell, the British representative at Berlin. Stanley himself said that he had been offered the choice of embassies to Madrid or St. Petersburg, and that he had accepted the latter ‘as a temporary retreat from the present confusion.’ Before Stanley left England the government's overtures were coldly received by Frederick of Prussia, and Stanley never took up the appointment (Chatham Corresp. iii. 15–174). On 24 March 1767 Grenville made a severe attack on Chatham for his magnificent plans for special embassies, and mentioned this case. Stanley, ‘a very warm man, retorted with vigour,’ as he had acted ‘with singular honour’ in waiving his right to the appointment (Walpole, George III, ii. 438–439).
On 4 Dec. 1766 Stanley was appointed cofferer of the household, an office which he temporarily vacated in 1774, but resumed in 1776 and held till his death. He had meanwhile resigned his post of governor of the Isle of Wight, but was reappointed to that office also in 1776. Afterwards the post was conferred upon him for life, an act without precedent at the time, and ‘it was said with an additional pension’ (Walpole, Last Journals, i. 327, ii. 362). In November 1768 he seconded the address to the king (cf. Cavendish, Debates).
Early in January 1780 Stanley paid a visit to Earl Spencer at Althorp. On the morning of 13 Jan. he cut his throat with a penknife in the woods, and died before assistance could be obtained.
Stanley's abilities were unquestioned, and his character stood high. Lady Hervey, who knew him well, called him ‘a very ingenious, sensible, knowing, conversable, and, what is still better, a worthy, honest, valuable man’ (Letters, 1821, pp. 204–332). He was awkward in appearance, ungracious in manners, and eccentric in his habits. He never laughed, and his speech is described by Madame Du Deffand as slow and cold without action, and as pompous without weight (Letters, 1810 edit. ii. 244–5). A bachelor, with ‘a large house in Privy Gardens, joining to Lord Loudoun's,’ and with the country residences of Paultons, which he inherited from his father, and Steephill, which he built at Ventnor, he spent most of his time away from them, ‘and when at home in town commonly dined at an hotel.’ He left a natural son at Winchester school. From his mother he inherited her share in the Sloane property at Chelsea. Paultons Square and Paultons Terrace at Chelsea perpetuate his connection with the parish. The estate of Paultons passed, subject to the life interest of Stanley's sisters, to a cousin, Hans Sloane, nephew of Sir Hans Sloane. Stanley was one of the trustees for the collection of Sir Hans, and was until death a family trustee of the British Museum.
Stanley left in manuscript various works, including a defence, written in Ciceronian Latin, of the English seizure of the French ships previous to the declaration of war. A poem of his in three cantos was imitated from Dryden's ‘Fables,’ and at the time of his death he was engaged in translating Pindar. Dr. Joseph Warton praised his knowledge of modern and ancient Greek (Pope, Works, 1797, ed. ii. 58–9), stating that he maintained a learned correspondence with the Abbé Barthelemy of Paris on the origin of Chaucer's ‘Palamon and Arcite.’ Many of his manuscript letters are in the British Museum Additional MSS. (22359 and 32734–33068), and most of his correspondence with Chatham is preserved at Paultons. Printed communications are in Belsham's ‘Life of Theophilus Lindsey’ (pp. 497–500) and ‘Life of Viscount Keppel’ (ii. 237). He was an intimate friend of Helvetius, much to the discontent of Gibbon, who complained in February 1763 of the excessive admiration enjoyed by Stanley in French society; and he was a pall-bearer at Garrick's funeral (Leslie and Taylor, Sir Joshua Reynolds, ii. 247).
His portrait as a young man, with long face and dark hair, was painted by Sir Joshua Reynolds, and is at Paultons. In 1765 there was published a profile engraving of ‘Hans de Stanley, dessiné par C. N. Cochin, le fils, gravé par S. C. Miger.’
[Gent. Mag. 1761 pp. 236, 475, 1764 p. 199, 1780 p. 51; Corresp. of George III and North, i. 213; Thomas Hutchinson's Diary, ii. 325–9; Albemarle's Rockingham, i. 21–76; Walpole's George III (ed. Le Marchant), i. 58–9, ii. 363–5; Walpole's Letters, ii. 443, iv. 352, 361–2, vi. 113,
