No terms were disclosed, but the Tampa (Fla.) Tribune said it was for one year.
He was given a tryout last week when back-up Luke McCown suffered a season-ending knee injury. Fiedler was limited to eight games in 2005 with the New York Jets because of a shoulder injury.
In his career, Fiedler -- who also has played for Miami, Philadelphia, Minnesota and Jacksonville after going undrafted out of Datmouth -- has completed 58.7 percent of his passes for 11,844 yards, 69 touchdowns and 66 interceptions. He also has rushed for 854 yards and 11 touchdowns.
Fiedler's 60 NFL starts make him the most experienced quarterback on the Bucs' roster.