Tomlin was under contract for the upcoming season with an option in place for 2013. The new deal adds three years to the contract.
Financial terms of the deal weren't released.
Tomlin, 40, is entering his sixth season as the Steelers' coach. He is the 16th coach in franchise history but just the third since Chuck Noll took over in 1969.
The team is 55-25 in the regular season under Tomlin, who has taken the Steelers to the playoffs four of the five seasons. That includes a win in Super Bowl XLIII and an appearance in Super Bowl XLV.
"We are pleased to announce that Mike Tomlin will remain with the Steelers for at least five more years," said Steelers President Art Rooney II. "Mike is one of the top head coaches in the National Football League and we are thrilled he will continue to lead our team as we pursue another Super Bowl title."
Tomlin said: "I am excited that I will continue to be the head coach of the Pittsburgh Steelers for years to come. I am grateful to the Steelers organization for the opportunity I have been given over the past five years to work and live in this great city, and I am excited to continue to work to bring another championship to the Steelers and the city of Pittsburgh."