Terms of the contract were not disclosed, but ESPN says the 33-year-old agreed to a one-year deal worth $3 million.
Schaub replaces Tyrod Taylor, who had backed up Joe Flacco for the past four seasons.
The quarterback has struggled the past two seasons, getting benched in Houston in 2013 and getting beaten out for the starting position by rookie Derek Carr in Oakland last season.
He’s had five interceptions returned for touchdowns in the past two years.
Before the dismal couple seasons, Schaub had a solid run of success for the Texans, recording four 4,000-yard passing seasons,and even went to his second Pro Bowl in 2012.