 Cathcart was born in Mount Murragh, County Westmeath, Ireland and emigrated to the North American colonies at eight years of age, under the care of a relative, Captain John Cathcart.He joined the American Revolution and at the age of twelve served on a privateer.Three years later, as a midshipman on "The Confederacy", he was captured by the British and imprisoned on the prisoner ships, "The Good Hope" and from which he escaped in 1782.