The 38-year-old Stefanski is just the second Browns head coach ever to win the award, joining Forrest Gregg, who was honored in 1976.
Cleveland had the NFL's longest playoff drought when Stefanski arrived during the offseason, but he put an end to it in spectacular fashion.
With Stefanski at the helm, the Browns went 11-5, marking their best record since going 11-5 in 1994. Cleveland also qualified for the playoffs for the first time since 2002 as well.
Although it didn't figure into the Coach of the Year voting, Stefanski also helped the Browns slay another major demon in the postseason, as they beat the rival Pittsburgh Steelers on the road in the AFC Wild Card Round.
In his second NFL season in 2019, quarterback Baker Mayfield took a step back compared to what he did as a rookie. Stefanski got him back on track in 2020, however, as he completed 62.8 percent of his passes for 3,563 yards, 26 touchdowns and eight interceptions.
Stefanski also presided over a dominant running game, as Cleveland ranked third in the NFL in rushing yards per game with 148.4 on the strength of Nick Chubb and Kareem Hunt.
Now that the Browns have finally made it back to the postseason, they could have even bigger and better things ahead with Stefanski running the show.