The Seahawks announced the move Saturday after it was revealed that quarterback Geno Smith needed a cyst removed from his knee. He was competing with Paxton Lynch for the backup job, but now will be sidelined for a week or longer due to the cyst.
The New Orleans Saints signed Barrett as an undrafted free agent in 2018. He spent time on and off the team's practice squad before being waived this month.
Barrett was selected to the All-Big Ten first team three times at Ohio State and broke numerous school passing records. He won a national championship with the Buckeyes in 2015.
The 24-year-old quarterback started 44 games for the Buckeyes and threw for 9,434 yards and 104 touchdowns, breaking New Orleans Saints star Drew Brees' conference record in career touchdown passes. He added 3,263 rushing yards and 43 scores on the ground.
The Seahawks also signed linebacker Juwon Young on Saturday. He played at the University of Miami before transferring to Marshall. He signed with the Detroit Lions this off-season but was waived in June.