The Chicago Bears selected Harris in the first round (14th overall pick) of the 2004 NFL Draft, and he played for the Bears from to . In 2004, he finished second in balloting for the Defensive Rookie of the Year award. In only his second NFL season, Harris was selected for the 2006 Pro Bowl for the first time. Harris was well suited for coach Lovie Smith's version of the Tampa 2 defense, which relies on quick, mobile linemen to get pressure on the quarterback.