November 17, 1718, he was appointed Envoy and Plenipotentiary to the Court of Turin; from whence he returned to Paris; and, May 31, 1719, set out for the Duke of Berwick’s camp before Fontarabia. After Admiral Byng had destroyed the greatest part of the Spanish fleet, Colonel Stanhope procured an English squadron to fall upon the port of St. Anthony in the Bay of Biscay, in which were one Spanish man-of-war of seventy guns, and two of sixty, newly built, with an incredible quantity of timber, pitch, and tar, and other naval stores, for building more; all which were destroyed by the English squadron, assisted by a detachment which the Duke of Berwick spared from his army, at the solicitation of Colonel Stanhope, who contrived the design, and, serving as a volunteer in the enterprise, principally contributed to the execution of it; where, finding it necessary to encourage and animate troops which had not been used to enterprises by sea, he was the first that leaped into the water when the boats approached the shore. At the end of that war he was declared a Brigadier-General, and returned with the same character as before to Spain. But the Spaniards having laid siege to Gibraltar, he left Madrid on the 11th of March, 1726, and his late Majesty was pleased, in May, 1727, following, to appoint him Vice-Chamberlain of his Household, and to command him to be sworn of his Privy Council. After his present Majesty’s accession, he was nominated first Ambassador and Plenipotentiary to the Congress at Soissons; and September 9, 1729, declared Ambassador to the King of Spain. On the 20th of November following, he was advanced to the degree of a Peer of Great Britain, by the title of Lord Harrington; and on the 13th of June, 1730, was constituted principal Secretary of State. December 18, 1735, he was declared Major-General of the Horse; and Lieutenant-General, July 17, 1739. His Lordship resigned the Seals, February 12, 1741-2, and the next day was declared Lord President of the Council. February 9, 1741-2, he was raised to the dignity of a Viscount and Earl of Great Britain, by the title of Viscount Petersham, Earl of Harrington. On the resignation of Earl Granville, October 18, 1744, his Lordship was again appointed principal Secretary of State; and in 1745 attended on his Majesty to Hanover. February 10, 1745-6, his Lordship resigned the Seals; but his Majesty was pleased to re-deliver them to him four days after. November 22, 1746, his Lordship was declared Lord-Lieutenant of Ireland, in the room of the Earl of Chesterfield, in which post he continued until 1771. March 22, 1746-7, he was constituted General of his Majesty’s Foot forces.