He was the son of William Kerr, 2nd Marquess of Lothian and Lady Jean Campbell.
He succeeded to the Marquessate of Lothian in 1722 and was elected a representative peer in 1731, sitting in the House of Lords until 1761.
From 1732 to 1738, Lothian was Lord High Commissioner to the General Assembly of the Church of Scotland, and he was appointed a Knight of the Thistle in 1734.
[1] In Edinburgh, around 1750, the Marquess constructed a town house off the lower Canongate, close to Holyrood Palace, which was named Lothian Hutt.
This provided a more convenient lodging when requiring to attand the Scottish Parliament or other social events in the capital.