Stanley was appointed Colonel of the North Hampshire Militia in August 1759 when it was first embodied during the Seven Years' War, but resigned in 1761 in favour of a diplomatic and political career.
[2] He was at that time a follower of the Duke of Newcastle, but Pitt enlisted his services, ‘from opinion of his abilities.’ Stanley set out for Calais to meet the French agent on 24 May 1761.
On 7 April 1763 he sent a spirited letter to George Grenville, who was then in office, and to whom he was then attached, declining a seat at the treasury, and setting out how his claims had been neglected.
He solicited and obtained in July 1764 the post of Governor of the Isle of Wight or Vice Admiral and constable of Carisbrook Castle.
Mary Hervey described the governorship as ‘a very honourable, very convenient employment for him, and also very lucrative.’ At Steephill Manor, on the site of the present castle, near Ventnor, he built a cottage in 1770 at considerable expense, and he entertained there several foreign ambassadors.