Charles Cathcart, 8th Lord Cathcart was a British Army officer. Before 1732 he was known as The Honourable Charles Cathcart. He was the second son of Alan Cathcart, 7th Lord Cathcart by his wife Elizabeth, daughter of James Dalrymple, 1st Viscount of Stair. His elder brother Alan died at sea in 1699. Cathcart joined the Army at the age of seventeen, and in 1704 he commanded a company in Colonel Macartney's regiment serving against the French on the frontiers of Holland. In 1706 he commanded a troop in the Scots Greys, which corps distinguished itself at the decisive Battle of Ramillies in the same year; and in 1707 he was brigade-major to the Earl of Stair. Continuing in active service, Captain Cathcart was at most of the general actions fought by the army commanded by the Duke of Marlborough, acquiring the reputation of a brave and zealous officer. In 1709 he was appointed major of the Scots Greys and shortly afterwards obtained the lieutenant-colonelcy of the regiment. On the accession of King George I he was appointed one of the grooms of the bedchamber.