The Ravens consider Mallett "a talented guy" and the risk-reward factor to be to their advantage in signing him through the 2016 season.
Mallett officially signed with Baltimore on Tuesday.
On Monday, coach John Harbaugh wouldn't confirm the signing but alluded to "personal things" Mallett "had to work through" since his release by the Texans on Oct. 27.
Texans coach Bill O'Brien was with theNew England Patriotswhen they selected Mallett in the third round of the 2011 draft and traded for him in2014. This season he was given the chance to compete for the starting position with Brian Hoyer.
O'Brien tolerated Mallett's missing a meeting the day after he was informed Hoyer won the competition but released the quarterback after he missed the team flight for Miami.
The Ravens have lost Joe Flacco for the season after knee surgery, and backup Matt Schaub has a chest injury. But the team didn't place Schaub on injured reserve Tuesday, and there is some hope he can play this week.
Mallett's role will be determined by how quickly he learns the offense with three weeks remaining in the season.
To make room for Mallett, the Ravens placed quarterbackBryn Renneron injured reserve.
ESPN.com's Jamison Hensley contributed to this report.
After getting help, Mallett signs with Ravens
ESPN Ravens reporter Jamison Hensley discusses why the Ravens waited to sign quarterback Ryan Mallett, and what his role will be with the team for the remainder of the year.