On the breaking out of the American Revolution he was induced by his friend and kinsman, Dr. Joseph Warren, to enter the medical department of the provincial army, although his inclinations led him in the direction of fighting in the ranks.

In the beginning he followed his bent and as a volunteer at the Battle of Lexington conducted himself with distinction, bearing from the field the body of the commander of the Brookline Company, Isaac Gardner, father of his future wife.

Receiving the appointment of surgeon to Gen. Heath's brigade and later deputy director to the army hospital in Jamaica Plain, Massachusetts, he rendered valuable service during the war.

For forty-five years he conducted a very large practice, most of the time going his rounds on horseback, and often covering forty miles in a day.

Gilbert Stuart painted his portrait, which was in the possession of his son-in-law, Lewis Tappan, a noted New York abolitionist, at the time when pro-slavery rioters broke into his home in 1834.