Vice-Admiral Lord Mark Robert Kerr (12 November 1776 – 9 September 1840) was an officer of the Royal Navy, the third son of William John Kerr, 5th Marquess of Lothian, by his wife Elizabeth, daughter of Chichester Fortescue of Dromisken.
Kerr served as a midshipman on HMS Lion, Captain Sir Erasmus Gower with Lord Macartney in his visit to China in 1792–1794, where he was commissioned as a lieutenant by Gower. He was present at the capture of Minorca in 1798. Captain Kerr was appointed to HMS Fisgard in September 1804, and a month later he captured several Spanish ships worth more than £14,000. On 2 November 1804, Horatio Nelson, himself quite ill, wrote to Lord Melville: '...I fear Lord M Kerr is falling into the same complaint [as I have]. I have now got him to the fleet and shall keep an Eye upon him for he is too valuable an Officer and good a Man to be lost for want of care.' 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 Orde who relayed the message to England.
Lord Mark Robert Kerr married on 18 July 1799 Charlotte (11 February 1778 – 26 October 1835), third daughter of Randal William Macdonnell, sixth Earl, and Marquess of Antrim; she succeeded him as Countess of Antrim (creation of 1785) in her own right on the death of her elder sister. They had a large family, two of their sons succeeding as fourth and fifth Earls of Antrim.