 Born in Philadelphia, Masterson attended Northeast Catholic High School and signed with the Senators at age 17.In 14 seasons he had a 78–100 win-loss record, 399 games (184 started), 70 complete games, 15 shutouts, 115 games finished, 20 saves, 1,649⅔ innings pitched, 1,613 hits allowed, 888 runs allowed, 760 earned runs allowed, 101 home runs allowed, 886 walks allowed, 815 strikeouts, 28 hit batsmen, 33 wild pitches, 7,281 batters faced, 1 balk, a 4.15 earned run average and a 1.515 WHIP.He missed the 1943 and 1944 seasons while serving in the Navy from September 1942 to July 1945 during World War II, serving on submarines in the Pacific.