The deal will be added to the one year remaining on his current contract and is worth $63 million, according to NFL Network's Ian Rapoport.
After flirting with retirement in recent years, Big Ben is now signed on to lead the Steelers until 2021, when he'll turn 39 years old.
Pittsburgh has anointed Roethlisberger the team leader, even in the face of criticism from former teammates Antonio Brown, Le'Veon Bell, and others.
He led the league in passing yards with 5,129 in the 2018 season, eclipsing the 5,000-yard mark for the first time in his 15-year career. The six-time Pro Bowler added a career-high 34 touchdown passes while throwing 16 interceptions.