After a long recovery from a frightening crash at the season-opening race at Daytona International Speedway, Busch took home the title in the final race at Homestead-Miami Speedway.
The 30-year-old Busch was top finisher in the Ford EcoBoost 400 championship, beating out contending drivers Kevin Harvick, Jeff Gordon and Martin Truex Jr.
"Pretty unbelievable. I just can't believe it with everything that happened this year," Busch told reporters.
Motor racing-Johnson crosses finish line of NASCAR career with full heart
09/11/2020 AT 00:22
"All the turmoil that I went through, that my family went through. This is for everyone that sacrificed so much to get me to this place today."
Harvick, the reigning champion, finished a distant second. Gordon took sixth in the final race of his decorated career, while Truex Jr. came in 12th.
After a caution flag late in the race, Busch was second with seven laps remaining but manoeuvred past leader Brad Keselowski and held on.
The end result looked like a distant dream early in the year when Busch's crash left him with a broken right leg and broken left foot.
Busch missed 11 races and NASCAR granted him a waiver to make the Chase provided he was able to win a race and crack the top 30 in points before the end of the 26-race regular season at Richmond International Raceway.
Busch met both requirements then held steady in the Eliminator Round with three top-five finishes to advance on points to the Championship 4.
Fellow driver Dale Earnhardt Jr tweeted congratulations to Busch and his Joe Gibbs Racing team.

NASCAR Cup Series 2020 Results
08/11/2020 AT 23:20
NASCAR Cup Series 2020 Results
01/11/2020 AT 23:10