William Cavendish 4th Duke of Devonshire KG PC (8 May 1720 – 2 October 1764) styled Lord Cavendish before 1729 and Marquess of Hartington between 1729 and 1755 was a British Whig statesman who was briefly nominal Prime Minister of Great Britain. He was the first son of William Cavendish 3rd Duke of Devonshire and Catherine Hoskins.