It was the first career title for Bell, who turns 23 next month and was the favorite to win the title Friday night at Homestead-Miami Speedway. Bell won five races this season driving a Toyota for Kyle Busch Motorsports and led the series in nearly every statistical category.
"There are no words to describe what this means to me," Bell said. "To be able to be here and to finish out my career at Kyle Busch Motorsports with the championship is something that I'm going to cherish for the rest of my life."
He wrapped up a second series driver championship for Busch, who will race for his second Cup title Sunday.
Bell finished second to Chase Briscoe, who raced to his first victory in the last event for Brad Keselowski Racing. The team is closing after this race and had a shot to end its run with a title behind Austin Cindric. But Cindric was beaten by Bell for the championship, so the team settled for the race victory with Briscoe.
"This is a long time coming," Briscoe said. "So proud of all these guys. To know that they're not going to have a job next year, and we continued to bring really good trucks, even though we were outside the playoffs, such a testament to how good these Brad Keselowski guys are.
"I know two years ago I was sleeping on couches, and now to be a winner in NASCAR ... it's been a long time coming."
Briscoe is a Ford Performance development driver, the first driver signed to the new program announced in January. His win was the first by a Ford Performance development racer since the program's inception. The program was launched with Keselowski, who will also race Sunday for a second Cup title.
"I feel that Chase is one of the best young talents ... so it is not a surprise to me to see him win a race and make the playoffs in his rookie year," Keselowski said. "It has been tremendous to have a role in continuing to develop top-tier talent in NASCAR. Chase is a driver that has that kind of future."
Johnny Sauter finished third but fell short in his bid to win a second consecutive title. Sauter announced a contract extension earlier Friday to drive for GMS Racing, the team he won the title with last year.
Cindric finished fifth and didn't have any of the issues others had threatened after his controversial advancement into the finale last week. He had an incident with Ben Rhodes that cost Rhodes a spot in the championship race, and some drivers had claimed there would be retaliation against Cindric at Homestead.
Nothing happened, and he was able to take some joy in teammate Briscoe's victory.
"I'm over the moon for the guys at BKR," Cindric said. "To get Chase a win after so many seconds he's had this year, it's a dream way to finish it out. Obviously, we wanted the championship, but we've come a long way in not a long time, so I'm proud of the effort and proud of how far we've come, and I'm looking forward to the future."
Two-time Truck Series champion Matt Crafton finished sixth. Only Bell, Sauter, Cindric and Crafton were racing for the title in a winner-take-all format.
Bell, meanwhile, races Saturday for the owner championship for Joe Gibbs Racing in the Xfinity Series finale. Bell will run full-time for Gibbs in that series in 2018.
Bell had 21 top-10 finishes this year in 23 races, and 15 top-fives.
"A dream come true just doesn't even describe it," Bell said. "For me to be at KBM as long as I have and to go out a champion there is something I'm really proud of. To be able to be standing here as a NASCAR champion is something I would say I dreamed of, but I didn't ever think it was a possibility, so I didn't ever really dream of it."
Toyota won its 10th manufacturers' championship, and fifth in a row. Toyota drivers won 12 races this season.