"Thank you so much for everything," she said after hugging runner-up Blake Lewis of Bothell, Wash.
A record 74 million votes were cast after Tuesday's competition round, "Idol" host Ryan Seacrest said.
"This Is My Now" is the song the selected by viewers in an online "American Idol" contest this season.
The nearly two-hour music extravaganza that preceded Sparks being named an "American Idol" included performances by several of the show's guest artists, including Tony Bennett and Gwen Stefani, and soul greats Smokey Robinson and Gladys Knight. Previous "Idol" winners Taylor Hicks, Ruben Studdard, Kelly Clarkson and Carrie Underwood also performed.
The evening raised a world social issue. Green Day performed John Lennon's hit "Working Class Hero" from "Instant Karma: The Campaign to Save Darfur," an effort to raise awareness and seek ways to end violence in the African country.