Culpepper never appeared fully recovered from major surgery in 2005 for three torn ligaments in his right knee. That injury had cost him the final nine games of the 2005 season.
A nine-year veteran, Culpepper's best season came in 2004 when he threw for 4,717 yards and tossed 39 touchdowns to just 11 interceptions, including 18 passes of 40 or more yards.
He has played in 85 career games, completing 64.2 percent of his passes with 137 touchdowns to 89 interceptions and a quarterback rating of 90.8.
The Raiders have called a noon press conference for Wednesday to announce the signing.