The 37-year-old country singer from Belton, Mo., beat runner-up Carly Rose Sonenclar, a 13-year-old schoolgirl from Westchester, N.Y., and teenage girl group Fifth Harmony on the finale that aired live Thursday night.
Stevens wins a $5 million recording contract with Epic Records.
For Stevens, a public works department employee, the X Factor was an opportunity to return to his first love. He gave up performing professionally when he and his wife had children. He auditioned for the show at their urging.
More than 35 million votes were cast by viewers after Wednesday's performance show.
Thursday's show was also the grand finale for Reid. Earlier this month, he said he wouldn't be returning to "The X Factor" next year. No replacement has been announced.
As Reuters reports, Reid, 56, chairman and chief executive of Epic Records, told "Access Hollywood," the television program and website, he has decided to leave the Fox reality singing show to return to the record label full time.
"I have decided that I will not return to 'The X Factor' next year," Reid told "Access Hollywood" on Dec. 12. "I have to go back and I have a company to run that I've kind of neglected, and it saddens me a little bit, but only a little bit."
He added that the show was "a nice break, it was a nice departure from what I've done for the past 20 years, but now I gotta go back to work."
Fox declined to comment on Reid's departure.
Cowell fired Abdul and Scherzinger after a disappointing first season and brought in pop stars Britney Spears and Demi Lovato.
But "The X Factor" audiences have dropped this year to an average 9.7 million from about 12.5 million an episode in 2011.
The show broadcasts a two-part finale next week with the winner earning a $5 million prize and record contract.
Epic Records, a unit of Sony Music Entertainment , which commands a roster of artists including Avril Lavigne, will sign the winners of "The X Factor."
(Reuters Reporting by Piya Sinha-Roy; editing by Jill Serjeant and Jeffrey Benkoe)