After 52 million votes were cast, the show's host Tyra Banks announced the 12-year-old ventriloquist as the 12th winner of the reality show.
After her performance on the first night of the live finals, Simon Cowell had predicted her as the winner.
“I think you’re gonna win,” he said.
For her final performance on show, Darci performed a duet of "Anything You Can Do" with ventriloquist Terry Fator, who won season two of "America's Talent."
Farmer beat nine other finalists including Nigerian plane crash survivor, Kechi Okwuchi, who had received a "yes" from each of the four judges after her first performance on the show.
With her subsequent performances, Kechi wowed and inspired the judges, viewers and her followers.
During an interactive session on Instagram, Kechi had asked her followers not to vote for her based on her story.
She also said she thinks it would be unfair if she emerges the winner.
Reacting to the results, Kechi, who finished 6th, said the winner and results were as she expected. She also took to Instagram to congratulate the winner and fellow contestants.
Other finalists include Evie Clair, Angelica Hale, Chase Goehring,Mandy Harvey, Sara & Hero, and LightBalance and Diavolo.
Farmer's win makes her the third female to win America's Got Talent ever.