He played for the Florida Marlins, Detroit Tigers, Texas Rangers, Kansas City Royals, and Los Angeles Dodgers.

Treanor attended Mater Dei High School in Santa Ana, California and was a standout baseball player.

As a senior, he was a second-team All-America pick and was named to the all-tournament team at the Upper Deck high school baseball tournament.

Treanor spent 10 years in the minor leagues–seven in Single-A[1]—before finally making his MLB debut on June 2, 2004 against the Cincinnati Reds, when he went 1 for 3 with a run scored.

On December 18, 2009, Treanor signed a minor league contract with the Milwaukee Brewers with an invitation to spring training, however on March 22 he was traded to the Texas Rangers in exchange for Ray Olmedo.

On June 15, Treanor returned to Florida to face his former team for the first time in interleague play, and hit a go-ahead two-RBI triple in the ninth inning and lifted the Rangers to a 3–2 win.

On December 17, 2013, Treanor signed a minor league deal, with an invitation to spring training, with the Cleveland Indians.

In November 2003, Treanor met beach volleyball star Misty May at a sports therapy facility in California.