The Honourable William Cathcart, Master of Cathcart (30 June 1782 - 4 June 1804) was a officer in the Royal Navy during the French Revolutionary and Napoleonic Wars. He was the eldest son of Scottish peer William Cathcart, 10th Lord Cathcart, later Earl Cathcart.
Cathcart joined the Royal Navy in August 1795 as a volunteer aboard HMS Melpomene. He was made a lieutenant on 2 September 1801. He served on HMS Medusa and was made master and commander on 14 April 1802. He then took charge of the sloop HMS Renard in October 1802, and then having been made post captain, took command of the frigate HMS Clorinde. He died in the West Indies of yellow fever while commanding her, on 4 June 1804 at the age of 22.[1]