The move comes after the Bengals finished 7-9 in 2017 during Lewis' 15th season at the helm, marking the second straight season the team missed the playoffs following five consecutive trips to the postseason between 2011 and 2015 that all resulted in losses in the Wild Card Round.
It's a particularly surprising move considering ESPN's Adam Schefter reported Dec. 17 that Lewis was "planning to leave the Bengals after this season to pursue opportunities elsewhere."
Following a 3-6 start that featured wins against the Cleveland Browns, Buffalo Bills and Indianapolis Colts, the Bengals finished 4-3 over the season's final seven games. That stretch included victories against the Detroit Lions and Baltimore Ravens over the final two weeks of the regular season.
And while a third-place finish in the AFC North is disappointing, Lewis can take solace in knowing that his defense was stingy at times and allowed a 16th-ranked 21.8 points per game.
That said, CBS Sports' Jason La Canfora reported Tuesday defensive coordinator Paul Guenther "is leaving to explore other options" after his contract expired.
The offense, meanwhile, encountered speed bumps galore after offensive coordinator Ken Zampese was fired and replaced by Bill Lazor two weeks into the season.
All told, Cincinnati ranked dead last in total offense (280.5 yards per game) with bottom-six marks in both rushing and passing.
In other words, Lewis will need to hunker down and help reconstruct the offense with the help of the front office if the Bengals are to look the part of a formidable AFC contender and return to the postseason in 2018.
"My job is to win a world championship," Lewis said Tuesday. "We have a talented roster full of veteran leaders and emerging young stars and I am committed to making the necessary improvements to put this team in the best position to win."