John McArthur spent a long career as an officer in the British Navy. He was commissioned as an assistant clerk on the HMS Eagle, before being promoted to purser (accountant) of the Rattlesnake and then the Santa Margarita. He served in these capacities during the American War of Independence, when he was often stationed to observe naval flag signals. His attempts to improve the signalling system brought him to the attention of Admiral Hood, who employed him as secretary and purser aboard his flagship, HMS Victory. By this time, McArthur had become known as a writer on military and naval issues. He later wrote a pioneering life of Lord Nelson. McArthur evidently acquired considerable wealth in his period of service, enabling him to become the proprietor of a valuable sugar plantation in Guyana. His prosperity is reflected in this stylish portrait by Romney, one of London's most fashionable portraitists, as well his purchase of paintings by the celebrated historical painters Benjamin West and Richard Westall.