The extension was expected because the Steelers' policy has been to sign a coach before he begins the final season of a contract. Tomlin's current contract, which averages $2.5 million annually, had one season and an option year remaining.
Financial terms of the extension weren't disclosed.
"Mike Tomlin has proven to be one of the top head coaches in the National Football League in a relatively short time," Steelers president Art Rooney II said in the statement. "His unique ability to lead the team and motivate individuals have been key factors in our success over recent years."
Tomlin led the Steelers to the 2008 Super Bowl title in his second year, becoming the youngest coach -- he was 36 -- to win it all when Pittsburgh beat Arizona 27-23.
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But in 2009, the Steelers finished 9-7, losing five in a row and missing the playoffs to become the first champion to miss out on the following postseason since the Steelers themselves in 2006.
Tomlin is only the Steelers' third coach since 1969, following Chuck Noll (1969-91) and Bill Cowher (1992-2006).
"I have been blessed to have the opportunity to be the head coach for the Pittsburgh Steelers," Tomlin said in the news release. "I am excited to have the opportunity to live and work in this great city, and to focus on the true matter at hand, which is winning football games and bringing another Super Bowl title to Pittsburgh."
The Post-Gazette had reported earlier this month that Tomlin and the Steelers had reached agreement on a three-year deal.
Information from The Associated Press was used in this report.
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