Terms of the one-year deal were not disclosed.
Leftwich missed the entire 2011 season after breaking his left arm in the preseason. The 32-year-old Leftwich has thrown just seven passes since the Steelers signed him in 2010.
Leftwich spent the first four seasons of his career with the Jacksonville Jaguars after being drafted seventh overall in the 2003 NFL draft. He moved to Atlanta in 2007, signed with the Steelers for the 2008 season and played for Tampa Bay in 2009 before returning to Pittsburgh.