The deal is for one year and $4 million, per Mike Garafolo of the NFL Network.
Blythe, 29, was a three-year starter for the Los Angeles Rams at both guard and center from 2018-20. He appeared in a total of 63 games with 48 starts during his four seasons with the team.
Blythe signed with the Kansas City Chiefs last season, but lost his starting job to rookie Creed Humphrey. He would play just 12 offensive snaps over four games for the team last season. He also dealt with a sports hernia that required surgery during training camp.
Blythe played for Seahawks offensive coordinator Shane Waldron with the Rams and comes to Seattle familiar with Seattle's desired offensive scheme and playbook.
He joined Dekoda Shepley as the only center currently listed on Seattle's roster. Ethan Pocic and Kyle Fuller are both free agents.
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