Grimes first joined the Falcons as an undrafted free agent out of Division II school Shippensburg University in 2006. He would be allocated to NFL Europe the following spring before making the Falcons practice squad the ensuing fall. He would be promoted to the roster in October 2007 and rise to become starter in 2008. He would lose the job before regaining it late in 2009 due to injuries and lead the team with 6 interceptions. He would become a Pro Bowler in 2010 and continued his high level of play again in 2011. But he suffered an Achilles tear in the season opener against the Kansas City Chiefs this past season, missing the remainder of the season.
Currently the leading candidate to start at cornerback opposite Asante Samuel is Robert McClain.