Gaither is brought in to replace Travis Goethel who was lost for the season with an ACL injury against the Ravens last week.
The 6-foot-1, 235-pound Gaither came into the league as the Eagle's fifth round pick out of Tennessee. He became the fulltime starter at middle linebacker in his second season and amassed 103 combined tackles (69 solo) during that season.
That was his only full season as a starter but he would play in 74 of 96 games the past six seasons. Gaither's career totals include 393 tackles (254 solo), 51 special-teams stops, six sacks, 25 passes defensed, two interceptions, one forced fumble and two fumble recoveries.
He was in training camp with Houston Texans this season but didn't make the final roster and his name has been floated about as a possible signee by the Raiders who have been thin at the linebacker position all season.
Gaither will wear No. 53 for the Raiders.
To make room on the team's active roster, the Raiders Wednesday officially placed LB Travis Goethel on injured reserve (knee).