The Commanders signed Wagner on Wednesday, Nicki Jhabvala of The Washington Post reports.
Wagner is expected to test the free agency market this week, Ian Rapoport of NFL Network reports.
Wagner finished with 11 tackles (eight solo), including a sack and two tackles for a loss, in the Seahawks' 20-17 win over the Titans on Sunday.
Wagner had 13 tackles (three solo) in Sunday's 24-20 win over the Browns.
Wagner registered nine tackles (six solo) in Sunday's 20-10 win over the Cardinals.
Wagner registered 19 tackles (nine solo) in Sunday's 30-13 loss to the Rams.
The Seahawks and Wagner agreed to a one-year, $7 million contract Saturday, Adam Schefter of ESPN reports.
The Rams and Wagner mutually agreed to part ways Thursday, Adam Schefter of ESPN reports.
Wagner logged seven solo tackles, a quarterback hit and a tackle for loss during the Rams' 19-16 overtime loss to the Seahawks.
Wagner recorded seven tackles (five solo) during Sunday's 31-10 loss to the Chargers.