LaHair was selected by the Mariners in the 39th round of the 2002 Major League Baseball Draft out of Saint Petersburg College.

LaHair spent the 2005 season with the Inland Empire 66ers, the Mariners' Single-A affiliate at the time, where he hit .310 with 22 home runs and 113 RBI, earning a spot in the California/Carolina League All-Star Game.

[1] The Mariners had called up infielder Tug Hulett directly following Sexson's departure, but sent him back down to make room for LaHair a week later.

His first Major League Baseball hit was a line drive single to right field against the Boston Red Sox.

On January 9, 2010, LaHair signed a minor league contract with the Chicago Cubs with an invite to spring training.

On July 1, 2012, Lahair, who then was hitting .284 with 13 home runs and 28 RBI, was named to the NL All-Star team as a reserve at first base.

Bryan LaHair was hired in January 2018 to be the Billings Mustangs hitting coach, the rookie ball affiliate of the Cincinnati Reds.