"Congratulations, Carrie," said host Ryan Seacrest. "You win."
"Thank you so much, everybody," said a tearful Carrie. She then sang her single, to be released June 14: "Inside Your Heaven."
Both finalists also received a brand new red Ford Mustang, while the winner alone received access to a private jet.
This season, a record 500 million votes were cast. The two hours of the final show, held at the Kodak Theatre in Hollywood, contained suspense, flashbacks – and plenty of filler – and included musical appearances by Lynyrd Skynyrd, Kenny G, Babyface and David Hasselhoff (who didn't sing), as well as a montage in which Paula Abdul kept telling fellow judge Simon Cowell to "shut up."
Simon, however, had nothing but praise for Bo's rendition of "Inside Your Heaven," a song that Carrie also had previously performed. "I think you did out-sing Carrie on this song," said Simon. "It has been absolute pleasure having you on American Idol."
When Carrie, 22, belted her final song, "Angels Brought Me Here" on Tuesday, Simon said: "You have a lot of guts. You're competing with someone who's older. ... Carrie, I think you've done enough to win this competition."
"This is the best night of my life. And it's going to get better," Underwood told the Associated Press after the show. As for the chance of her going Hollywood, don’t bank on it. She says she still wants her "permanent address to be in Oklahoma. … Someday, when I get married and I have kids, that's where I want to raise my kids."
Some observers called this season's competition the toughest since Ruben Studdard and Clay Aiken fought for the hearts of the American public two years ago. Ultimately, Studdard won the vote, but Aiken won the sales charts.
The other two previous Idol winners were Kelly Clarkson (while her runner-up, Justin Guarini, fizzled on the pop charts) and Fantasia Barrino, who had a 1.3-million-vote edge over Diana DeGarmo when the results were announced exactly a year ago.