Lewis, who spent the last two seasons coaching the secondary in Carolina, becomes the latest Panthers assistant to leave the organization. Linebackers coach Ken Flajole left to become the St. Louis Rams' defensive coordinator earlier in the week. Lewis' contract ran through the 2008 season.
The Seahawks were looking for a secondary coach after Jim Mora vacated the position to become head coach.
Lewis and assistant secondary coach Larry Marmie will oversee a once-promising unit that fell off in performance last season. Cornerback Marcus Trufant was a Pro Bowl starter after the 2007 season. Cornerbacks Kelly Jennings and Josh Wilson were also early draft choices.
The Seahawks ranked 25th in total defense and 31st in passing yards allowed and intercepted only nine passes all season. Carolina ranked 18th in total defense and 16th in passing yards allowed and picked off 12 passes.
Lewis was the 11th overall pick in the 1983 draft by Green Bay. He played four seasons as a defensive back for the Packers before a neck injury cut short his career in 1986.
ESPN.com NFL blogger Mike Sando covers the NFC West. Information from The Associated Press was used in this report.