John Johnston was born in Boston, the son of engraver and decorative painter Thomas Johnston (c. 1708-1767). Of four brothers who became painters, John Johnston was the most talented. He was apprenticed after his father's death to coach and heraldic painter John Gore. In 1773 he joined his brother-in-law Daniel Rea, Jr. in the painting firm of Johnston and Rea, a continuation of his father's business. Account books of the firm (Baker Library, Harvard University Business School) indicate that much of his work was decorating clock faces, furniture, fire buckets, coaches, and other objects. Johnston served in the continental army during the Revolutionary War, was severely wounded at the battle of Long Island in 1776, and was imprisoned by the British for about a year.
