The deal also includes a team option for the 2013 season. Financial details weren’t disclosed.
Tomlin, 38, led the Steelers to the Super Bowl championship after the 2008 season, his second year in charge of the National Football League team. He has a career regular-season coaching record of 31-17.
The Steelers failed to make the postseason last year, and will be without quarterback Ben Roethlisberger for the first six games of this season. Roethlisberger was suspended by the league after a series of off-the-field legal problems.