Losman's agent, Gary Wichard, confirmed the deal in an e-mail to The Associated Press on Tuesday night. The Seahawks officially announced the deal Wednesday and said it was signed, although they didn't disclose terms.
Foxsports.com first reported the agreement between Losman, the Bills' 2004 first-round draft pick, and the Seahawks, who are loading up with competition at every position -- including the most important one.
Three-time Pro Bowl quarterback Matt Hasselbeck is 34 and entering the final season of his contract. He threw a career-high 17 interceptions last season while being battered for a second consecutive year.
The Seahawks recently traded two draft picks and then gave an $8 million contract to former San Diego Chargers third-stringer Charlie Whitehurst to have him challenge Hasselbeck now -- and eventually replace him.
"I am real pleased with Matt being our quarterback right now and being in the lead position," Carroll said Monday. "However, we are trying to make it as competitive as possible. We are trying to push Matt to make him better and try to elevate Charlie's game as well. That is just the way we are doing it. It will always be a competition in my mind."
Third-string quarterback Mike Teel tweeted Wednesday night that he had been released by the Seahawks.
Losman's agreement with the Seahawks came hours after the team released Mike Reilly, the former record-setting passer at Central Washington whom they had claimed two weeks ago off waivers from the St. Louis Rams to compete for the No. 3 job.
Losman's only full season as a starter was 2006 -- not counting his 2009 UFL championship season with the Las Vegas Locomotives. Known for his strong arm, Losman threw 19 touchdown passes and 14 interceptions in '06 for Buffalo. The Bills then drafted Trent Edwards, and Losman soon wanted out of town.
At wide receiver, Carroll has signed Reggie Williams and Mike Williams out of free-agent tryouts. Both are failed former top-10 overall picks who have a new NFL life behind leading receiver T.J. Houshmandzadeh.
The Associated Press contributed to this report.