[1] His paternal grandparents were William Kerr, 4th Marquess of Lothian and Lady Caroline D'Arcy (a daughter of the 3rd Earl of Holderness and a scion of the House of Schomberg).

[2] His maternal grandparents were Chichester Fortescue of Dromisken, who represented Trim in the Irish House of Commons, and the Hon.

Captain Kerr was appointed to HMS Fisgard in September 1804, and a month later he captured several Spanish ships worth more than £14,000.

In April 1805, Captain Mark Kerr discovered that the French Toulon fleet, sought by Nelson, were in the Atlantic and he passed this information on to Vice-Admiral John Orde, who relayed the message to England.

Lord Mark Kerr died on 9 September 1840 at his residence in Henrietta Street, Cavendish Square, London.