Leary posted a 10–2 record in his senior year at Santa Monica High School, and was named to the 1976 All-California Interscholastic Federation first-team.

[1] Much more in stature than his teammate and fellow former major leaguer, Rod Allen, he received the opportunity to play college baseball at UCLA.

[2] In 1978, Leary helped lead the United States national baseball team to the silver medal in the World Cup played in Italy.

Making his major league debut on April 12, 1981, Leary faced just seven batters,[4] before leaving the game after just two innings with a strained elbow.

Regardless, he received a second call up to the majors that September, and never made it out of the second inning in his return, mostly due to two errors by George Foster in left field that led to five unearned runs.

Leary spent the 1985 season with Milwaukee's triple A affiliate, the Vancouver Canadians, and once again returned to the majors when rosters expanded that September.

[11] He finished the season second on his team behind Cy Young Award winner Orel Hershiser in wins (17), ERA (2.91), shutouts (6), complete games (9) and innings pitched (228.2), while leading his club with 180 strikeouts.

[15] Following the Dodgers' World Series victory, Leary was named the Sporting News' National League Comeback Player of the Year for his regular season performance.

After the season, the Reds sent him and Van Snider to the New York Yankees for Hal Morris and minor leaguer Rodney Imes.

He was moved back into the starting rotation in 1992, and was 5–6 with a 5.57 ERA when he was dealt to the Seattle Mariners for minor leaguer Sean Twitty.

In 1993, the Mariners improved from a team that narrowly avoided one hundred losses to 82–80, mostly due to new manager Lou Piniella, and the emergence of young stars Randy Johnson, Ken Griffey Jr. and Jay Buhner.