Cathcart joined the army in America in 1776, serving as a volunteer until commissioned in the 23rd Foot. Sailing from New York to the 77th Foot in Ireland, he was captured by a French privateer, and on his release was commissioned in 1780 second in command of the 98th Foot then raising under William Fullarton. From 1781 he served in India and in June 1783 distinguished himself against the French at Cuddalore.
In the House he spoke in the East India debates on 2 and 19 July 1784. He praised Hastings’s ability and integrity, and, concentrating on military organization, urged a clear definition of the status of commanders-in-chief in relation to the civil administration.
