McClain was selected with the 137th pick during the fourth round by the Baltimore Ravens.[5]
McClain signed with the Ravens on July 27, 2007. He scored his first career touchdown on a Kyle Boller pass against the San Diego Chargers on November 25, 2007. He finished his rookie season with eight carries for 18 yards, nine receptions for 55 yards, and 1 touchdown.
During the 2008 season, McClain became the team's primary running-back as he rushed for a team-high 902 yards and 10 touchdowns on 232 carries (3.9 yards per carry). He also caught 19 passes for 123 yards and a touchdown. On December 20, 2008, McClain ran for 82 yards to score the final touchdown in Texas Stadium against the Dallas Cowboys. Along with teammate Willis McGahee's 77-yard touchdown run on the previous Ravens drive, he and McGahee became the first players ever to run two 70+ touchdown runs on back-to-back drives. The run was also the longest run by an opponent in Texas Stadium. In addition, McClain had 139 rushing yards on the day. McClain's performance earned him a Pro Bowl selection, in which he scored a touchdown off of a Fumblerooski play handed off by former Denver BroncosquarterbackJay Cutler. Cutler put the ball between McClain's legs in which he ran in for a touchdown.
During his last two years as a Raven, McClain lost carries to Willis McGahee and Ray Rice. He publicly complained about not getting enough touches, which led to his departure from the Ravens.