John H. Mason was born in Boston on October 24, 1945. He graduated from Harvard College, with honors, in 1967. After law school, he volunteered for the Army during the Vietnam War, attending Officer Candidacy School and serving as an advisor to Vietnamese combat troops. He earned a Bronze Star for his service. After his military service, he attended the University of Pennsylvania Law School, where he was editor-in-chief of the Pennsylvania Law Review. He graduated, magna cum laude, in 1973.
Justice Mason began his legal career as a clerk for Judge Walter Mansfield of the United States Court of Appeals for the Second Circuit. Afterwards, he practiced at the firm of Ropes & Gray for over a quarter century, first as an associate and then as a partner. He specialized in labor and employment law, litigation, and civil rights. In 2001 he was appointed to the Appeals Court by Governor Paul Cellucci. Justice Mason passed away on July 17, 2004. The Appeals Court's Memorial to Justice Mason may be found at 64 Mass. App. Ct. 1115 (2005).