William Murray was born on 14 April 1689, at Huntingtower near Perth, Scotland, second son of John Murray, 1st Duke of Atholl (1660–1724) and his first wife, Katherine Hamilton (1662–1707). One of more than 20 children, when his elder brother John was killed at Malplaquet in August 1709, he became Marquess of Tullibardine and heir to the dukedom. After he was attainted for his part in the Jacobite rising of 1715, his younger brother succeeded as James succeeded as Duke of Atholl in 1724.