Tomlin, who is beginning his 11th season with the franchise, has a 103-57 regular-season record. He has never experienced a losing campaign and guided the Steelers to a Super Bowl title in his second year as coach.
Pittsburgh, which has made two Super Bowl appearances during Tomlin's reign, has won 10 or more games in each of the last three seasons.
"I truly appreciate this contract extension, and I want to thank (team president) Art Rooney II for his support as well as everyone within the organization," Tomlin said in a statement. "My first 10 years in Pittsburgh have been an amazing experience for me and my family. I'm proud to call Pittsburgh home.
"My focus is on the upcoming season, and our goals remain the same as they always are -- to bring a seventh Super Bowl championship back to our city."
The 45-year-old Tomlin is one of just three people to coach the Steelers since 1969, following Chuck Noll and Bill Cowher. He reached 100 career victories in the fewest games (157) in franchise history when he recorded the milestone win last season.
"Mike continues to prove he is one of the top head coaches in the National Football League," Rooney said in a statement. "We appreciate the leadership that Mike has provided over the last 10 seasons, and we are confident and excited to have him continue to lead our team as we focus on winning another championship."
Pittsburgh has won five AFC North titles under Tomlin. The Steelers have made seven postseason appearances during Tomlin's tenure.