Mayowa's agent, David Canter, announced the agreement Wednesday. It's a one-year deal worth $3 million, a source told ESPN.
The Seahawks are not believed to be finished adding pass-rushers, whether that means Clowney or one of the other free agents who remain unsigned.
Mayowa, 28, recorded a career-high seven sacks and three forced fumbles on only 270 defensive snaps in 15 games last season with the Raiders. It was his second stint in Oakland, where he spent the 2014 and '15 seasons. Mayowa began his career with Seattle as an undrafted free agent out of Idaho in 2013. He has also played for Dallas and Arizona, and he has 20 career sacks in 87 games.
Earlier in free agency, the Seahawks brought back another of their former defensive ends in Bruce Irvin as they try to improve what was one of the NFL's least effective pass-rush units in 2019. Irvin had a career-high 8.5 sacks last season with Carolina. Clowney had three sacks for Seattle, and no Seahawks defender had more than four. The team finished the regular season with 28 sacks, tied for second fewest in the league.
Seattle also re-signed defensive tackle Jarran Reed, who had 10.5 sacks in 2018 and two in 10 games last season.
The deal with Mayowa came together quickly on Wednesday, a source told ESPN. Earlier Wednesday, sources told ESPN's Dianna Russini that Clowney's asking price had dropped at least $2 million off the more than $20 million per season he had been seeking.
Titans general manager Jon Robinson said Wednesday that the team has been in touch with Clowney's agents.