A versatile athlete, he played quarterback for Atascadero High School in Atascadero, California, and signed a National Letter of Intent to play football for the University of Southern California before being drafted by the Baltimore Orioles.

Over the course of his professional career, McClain achieved a total of 359 home runs, with 287 coming in the minors, 71 in Japan, and two in MLB.

McClain hit his first home run in the major leagues on September 3, 2008, while playing for the Giants against the Colorado Rockies at Coors Field.

While playing for the Oakland A's Triple-A affiliate, the Sacramento River Cats, in 2006, McClain won the Pacific Coast League Most Valuable Player Award.

McClain spent the 2007 and 2008 seasons with the Fresno Grizzlies, Triple-A affiliate of the Giants.