In two seasons at Valley Forge, he recorded 39.5 sacks and was first-team NJCAA All-America and Seaboard Conference Defensive Player of the Year as a sophomore.

Peterson played college football at Michigan State University for his junior and senior year.

[4] In six seasons in San Francisco he recorded 394 tackles, 21.5 sacks, and five interceptions in 79 games and was elected to two Pro Bowls.

In his third season with the team, Peterson made 86 tackles and five sacks, and was selected to his third consecutive Pro Bowl.

The Seattle Seahawks traded Peterson to the Detroit Lions for defensive tackle Cory Redding and a 2009 fifth-round pick on March 14, 2009.