Newcastle, Thomas Pelham-Holles, duke of, 1693–1768, English politician, brother of Henry Pelham. He inherited (1711) the estates of his uncle, John Holles, duke of Newcastle, adopted his name, and received (1715) his title. In 1724 he became secretary of state under Sir Robert Walpole, and he retained that position after Walpole's fall and through his brother's long ministry (1743–54). In 1754 he succeeded his brother as first lord of the treasury, or prime minister. His weak policy in the Seven Years War led to his resignation in 1756, but the next year he returned to power as nominal head of a coalition ministry with William Pitt, later 1st earl of Chatham. Forced (1762) out of office by George III's favorite, Lord Bute, he later served (1765) as lord privy seal under the marquess of Rockingham. Newcastle was ineffective and irresolute in his conduct of public affairs, but he wielded immense political influence through his clever use of patronage, helping to provide parliamentary majorities for Walpole, Pelham, and Pitt.
See B. Williams, Carteret and Newcastle (1943, repr. 1966); J. B. Owen, The Rise of the Pelhams (1957, repr. 1971); R. A. Kelch, Newcastle; A Duke without Money (1974); R. Middleton, The Bells of Victory: The Pitt-Newcastle Victory and the Conduct of the Seven Years' War (1985).