The NFL's all-time leading rusher beat out actor Mario Lopez.
The hunky, dimpled Lopez was generally regarded as the series most dynamic celebrity dancer, but the public's vote, the deciding factor after the contestants had tied in the judges' tally at Tuesday's final dance-off, brought Smith the victory.
"It is awesome! It is awesome!" declared Smith, after hugging his professional dance partner Cheryl Burke. "We came a long way, we really have."
Burke won last season, too, on the arm of singer Drew Lachey.
Smith had kind words for Lopez, who was gracious in his defeat. He called the former "Saved by the Bell" star a "true gentleman" and said he and partner Karina Smirnoff "raised the bar" during the competition.
"This whole journey was unbelievable ... And Karina, most unbelievable person," Lopez gushed. "It's something I'll never forget."
Smith and Burke wowed judges on Tuesday with a spirited samba, to the tune of Stevie Wonder's "Sir Duke."
"What's so great about you is you are the everyday man who became a dancer in our eyes in the past 10 weeks," judge Carrie Anna Inaba told Smith, who's been dubbed "The Big Easy" for his laid-back elegance and charm.
In the closing segment of Wednesday's decision show, Burke, in a video clip, praised Smith's work ethic.
"From the beginning, he just wanted to be the best possible dancer he can be," she said.
Smith, ever the competitor, was determined to bring home the show's mirror ball trophy. "You don't get into a competition unless you think you can win," he told AP Radio after Tuesday's dance finale.
During Wednesday's program, all nine of the previously rejected celebrities — Vivica A. Fox, Harry Hamlin, Joey Lawrence, Sara Evans, Willa Ford, Monique Coleman, Jerry Springer, Tucker Carlson and former beauty queen Shanna Moakler — returned for a last dance with their partners.