A much-traveled, hard-throwing righthander, McGaffigan was the Southern League Pitcher of the Year at Nashville in 1980 (15-5, 2.38) and made his major league debut with the Yankees in 1981 before becoming one of two prospects traded to the Giants for Doyle Alexander in the spring of 1982. McGaffigan started occasionally for the Giants in 1983, then was traded twice in 1984, first to Montreal and then to Cincinnati. He started exclusively for the Reds in 1985 and fanned 11 Astros on August 1.
McGaffigan was traded back to Montreal after the season in a six-player swap where he served as an effective set-up man for bullpen ace Tim Burke, going 16-3 with 18 saves from 1986-88. After struggling in 1989, McGaffigan was dealt to the Giants, but he was released two weeks later. Signing with Kansas City, he started for the first time in three years and went 4-3 over his last two major-league seasons.
McGaffigan, who had just six hits in 126 major-league at-bats for an .048 average, was considered to be one of the worst-hitting pitchers of all time.