The Lions also are sending the Seahawks a fifth-round draft choice to complete the deal.
Redding signed a seven-year, $47.8 million contract to stay in Detroit in 2007, when the team decided to move him from defensive end. Former Lions coach Rod Marinelli believed Redding would be able to help the "three-technique" defensive tackle format.
Though Redding didn't produce the desired sacks, he is considered a talented, developing player who is still in his prime.
In acquiring Peterson, the Lions are getting a Pro Bowl-caliber linebacker who can get to the quarterback.
This week, the Seahawks asked Peterson to take a pay cut. He rejected that request and trade talks started around the league. The Lions moved quickly.
Peterson has 46 career sacks and has been to five Pro Bowls. He signed a seven-year, $54 million contract to join the Seahawks in 2006.
John Clayton is a senior NFL writer for ESPN.com. ESPN.com's Mike Sando contributed to this report.