Having served as a masters mate aboard the Phoenix 44, Captain Hyde Parker, Clark was commissioned lieutenant on 22 December 1776 and immediately placed in command of the galley Dependence 7 at New York. This vessel enjoyed many engagements against the Americans, although during one foray ashore Clark was wounded whilst blowing up a store when acting under the orders of Captain Sir James Wallace.
He was promoted commander on 2 August 1780, and in May 1782 commissioned the brand new Cato 50, initially being ordered to join Rear-Admiral Sir John Lockhart Ross in the North Sea, and being posted captain on 9 July,
In October 1782 the Cato departed for the East Indies with the flag of Vice-Admiral Sir Hyde Parker. She was at Rio de Janeiro on 12 December, but subsequent to leaving that port it was assumed that she was lost in the Indian Ocean sometime during January 1783. Various stories relating to her fate surfaced, including one that she had been wrecked on the Malabar Coast and all her men slaughtered, but in all probability she had simply caught fire and foundered at sea.