Leftwich, 28, signed a one-year, $605,000 deal to join the Steelers. Because he signed for a minimum exception contract, the deal will only count $445,000 on the Steelers salary cap. Leftwich was chosen over Daunte Culpepper, who also visited the Steelers Sunday.
The need for a backup quarterback was created when backup Charlie Batch suffered a broken right collarbone Friday night against the Philadelphia Eagles. Batch is expected to be sidelined four-to-six weeks.
Steelers coach Mike Tomlin said Leftwich, who has started 46 career games for Jacksonville and Atlanta, may not be released when Batch returns.
"We're just going to let the play talk," Tomlin said. "You know how we do it. We're going to evaluate what we see based on performance."
The reason the Steelers picked Leftwich over Culpepper is because Leftwich felt more comfortable with the role the Steelers were offering. Ben Roethlisberger is the starter and Batch is expected to be the backup when he gets healthy again. Culpepper was hoping for a chance to compete for a starting job.
Leftwich was released by Atlanta in February and has played in just nine games the past two seasons because of ankle injuries. A first-round pick of Jacksonville in 2003, he saw action in 15 games that season, making 13 starts. He missed two games in 2004 and five in 2005 with injuries.
A serious ankle injury in 2006 limited him to just six games, opening the door for backup David Garrard to get a 10-game audition and win the starting job. Leftwich was released at the end of training camp last year and signed with Atlanta.
Berger agreed to a one-year, $830,000 contract. Punter Daniel Sepulveda suffered a torn ACL and is out for the season. The Steelers claimed Paul Ernster on waivers from Detroit last week. Berger's deal will only count $445,000 against the Steelers salary cap.
The Associated Press contributed to this report.