He was a younger son of John Stanhope of Elvaston, Derbyshire, and a brother of Charles Stanhope (1673-1760), an active politician during the reign of George I. His ancestor, Sir John Stanhope (d. 1638), was a half-brother of Philip Stanhope, 1st Earl of Chesterfield. Educated at Eton, William Stanhope entered the army and served in Spain, during the War of the Spanish Succession, but soon he turned his attention to more peaceful pursuits, went on a mission to Madrid and represented his country at Turin.
When peace was made between England and Spain in 1720 Stanhope became British ambassador to the latter country, and he retained this position until March 1727, having built up his reputation as a diplomatist during a difficult period. In 1729 he had some part in arranging the Treaty of Seville between England, France and Spain, and for his services in this matter he was created Baron Harrington in January 1730.
Later in the same year he was appointed Secretary of State for the Northern Department under Sir Robert Walpole, replacing Lord Townshend, but, like George II, he was anxious to assist the emperor Charles VI in his [[War of the Polish Succession|war with France, while Walpole favored a policy of peace. Although the latter had his way Harrington remained secretary until the great ministers fall in 1742, when he was transferred to the office of Lord President of the Council and was created Earl of Harrington and Viscount Petersham.
In 1744, owing to the influence of his political allies, the Pelhams, he returned to his former post of Secretary of State, but he soon lost the favor of the king, and this was the principal cause why he left office in October 1746. He was Lord Lieutenant of Ireland from 1747 to 1751, and he died in London on 8 December 1756.
This article originally from the 1911 Encyclopedia Britannica.