On April 29, 2007, he became the first player in FIU history to be drafted by a National Football League team when he was selected in the fourth round with the 134th overall pick by the Baltimore Ravens.

During a 2007 preseason game, Barnes delivered a blind side hit on Philadelphia Eagles punter Sav Rocca, knocking off his helmet.

In 2009, Barnes started the year with his first career interception (against the San Diego Chargers, his future team), but then saw no action for several games.

The team finally started using him late in the season, with the defense having struggled with its pass rush, and he came in and notched 3 sacks and 10 solo tackles, as well as a forced fumble.

In the 2011 season, he established himself as one of the top pass rushers on the Chargers team, starting 5 games, and notching 41 tackles, 11 sacks, and 2 forced fumbles.