After a standout basketball career at Jackson's Provine High School, he signed a football scholarship with Mississippi State University, where he played in 22 games and earned 16 starts, making 82 tackles, including 15 for loss and two quarterback sacks.

After being signed in 2004 by the Oakland Raiders as an undrafted rookie free agent, Tommy Kelly alternated between 3–4 DE and 4–3 DT.

[4] On February 28, 2008, the Oakland Raiders signed Kelly to the largest contract ever given to a defensive tackle on the eve of free agency.

[5] Kelly can play every spot on the defensive line, but he replaced the retired Warren Sapp at the three technique for the 2008 NFL season.

In week 10, he recorded 3 tackles, a game-ending sack and a forced fumble as the Raiders beat the San Diego Chargers.

The next week, when the Raiders won against the Minnesota Vikings, he recorded 3 tackles, two sacks and an interception off of a deflected pass.