He was the eldest son of Scottish peer William Cathcart, 10th Lord Cathcart (1755 – 1843), later Earl Cathcart, and of Elizabeth Elliott (1760 – 1847), the daughter of Andrew Elliot, the governor of New York.[1] His younger brother was General, the Honourable Sir George Cathcart KCB DL (1794 – 1854).[2] Born in London, his birthdate is alternatively recorded as 13 June 1782, according to other sources.[3][1] Cathcart was educated in the paternal tradition at Eton College, Windsor, Berkshire, United Kingdom.[1]