Gamel attended Bishop Kenny High School in Jacksonville, Florida. He was drafted in the 2005 Major League Baseball Draft from Chipola College in Marianna, Florida. He was also known as 'the kid who got hit by a car and got a ticket for it', as he was struck by a vehicle while riding a bike through a crosswalk, and received a ticket for it.
He played his first professional season in 2005 for Milwaukee's Rookie League Helena Brewers. Gamel was promoted to the Single-A West Virginia Power in 2006 and the High Single-A Brevard County Manatees in 2007. He played most of the 2008 season with the Double-A Huntsville Stars before being promoted to the Triple-A Nashville Sounds on August 24. In 2008, he was selected to play in the All-Star Futures Game. He was hyped by some as "the next Ryan Braun".
Gamel was called up to the Majors for the first time when rosters expanded on September 1, 2008, and made his debut two days later, striking out in a pinch-hitting appearance. He recorded his first career hit, a double, on September 7, 2008, off of Chris Young of the San Diego Padres. He hit his first career home run on May 18, 2009, off of Kyle Lohse of the St. Louis Cardinals. However, he made his first fielding error at third base during the same game, even though he had made a great play just a few innings earlier. He hit his second home run off Jason Hammel of the Colorado Rockies.