Following the death of his nephew in 1729 (his elder brother predeceased their father in 1721), he inherited the earldoms of Leven and Melville, though he did not use the latter title.
Lord Leven served as a Lord of Session from 1734 to 1754; Grand Master of Scottish Freemasons 1741 to 1742; High Commissioner to the General Assembly of the Church of Scotland from 1741 to 1753; a Representative Peer for Scotland from 1747 to 1754; and a Lord of Police 1754.
On 23 February 1721, he married Mary Erskine, a daughter of Col. Hon. John Erskine of Carnock (third son of David Erskine, 2nd Lord Cardross) and Anna Dundas (daughter and co-heiress of William Dundas of Kincavel). Before her death in 1723, they had one child:[3]
After the death of his first wife in 1723, he married Elizabeth Monypenny, a daughter of Alexander Moneypenny of Pitmilly, on 13 March 1726.[5] They had four children: