In 2004, Thomas started all 16 games for the first time in his career. While still collecting 16 special teams tackles, he amassed 72 tackles, 4 forced fumbles, 5 passes defended, an interception and 8 sacks. In 2005, with Boulware relegated to situational pass-rush duty, Thomas was named the starting outside linebacker, where he accumulated 84 total tackles and 9 sacks. He also saw limited time at cornerback during that season. He had two interceptions on the year and three forced fumbles; he returned three turnovers for touchdowns, making him the NFL's leader in non-offensive touchdowns that season.