Clausen became only the sixth quarterback in NFL history to start against the same team for two different clubs in one season. His only other start this year came against the Seahawks on Sept. 27 -- a forgettable 26-0 loss -- while he was with the Chicago Bears.
Schaub was put on the team's inactive list for Sunday's game.
Clausen, 28, practiced with the Ravens' first-team offense all week, as Schaub was sidelined with a chest injury. Bryn Renner, who was out of football this season before joining the Ravens on Tuesday, was promoted from the practice squad Saturday and served as the backup.
This marks the third different starting quarterback in four weeks for the Ravens after Joe Flacco had started the previous 122 consecutive regular-season games, the fifth-longest streak in NFL history. Flacco tore two knee ligaments on Nov. 22, ending his season.
Clausen is now 1-12 as an NFL starter. His only victory came in December 2010, when he was a rookie with the Carolina Panthers.