Trent Harmon was crowned as the winner of the 15th and final season.
The show opened with President Barack Obama using the audience votes on "Idol" to point out the need to register to vote.
"Not all of us can sing like Kelly Clarkson but all of our voices matter," the President said while encouraging folks to head over to Vote.gov to register. "This show reached historic heights not only because Americans watched it, but because you participated in its success."
That was followed by blasts from the past including host Brian Dunkleman who famously left the show after the first season as well as former contestants and Season 8-9 judge Kara DioGuardi who took to the stage to perform. Season 1 winner Kelly Clarkson pre-recorded a medley of some of her biggest hits, because she is near to giving birth to her second child.
The show is ending after 15 seasons, juggernaut ratings (which fell off in recent years), thousands of aspiring superstars and way too many covers of Whitney Houston songs.
Thursday night's send-off is, without a doubt, a historic moment for television.
"Idol" was a shining star, more popular than any other regularly scheduled American TV series since the turn of the century.
It smothered the competition. It changed the Fox network's fortunes and spawned countless competitors and ripoffs around the world. In TV, that's magic.
Even today, "Idol" is a force to be reckoned with. Part one of the finale on Wednesday averaged 10 million viewers, impressive by 2016 standards but still a reminder of how far it's fallen. A decade ago, "Idol" drew 20 million, 30 million, even 40 million viewers.
The broadcast took place at the same Hollywood theater where Clarkson was crowned the winner at the end of season 1, in the summer of 2002.
Kieran Healy, the show's lighting director since the very beginning, said he's been dreading the finale.
"When Ryan says 'Dim the lights' for the last time, I'll probably be quite choked up," Healy said.
And he won't be alone.
Fans around the world took to social media to mourn the end of the "Idol" era.
So why is "Idol" ending now? Because it kept getting more and more expensive to produce while reaching fewer and fewer people. Fox has wagered that retiring the brand makes more sense than trying to keep it going.
People associated with the show admit that the time feels right for a series finale.
And yet some of them are confident this is just a break.
The show's creator, Simon Fuller, is already plotting a comeback, telling The Hollywood Reporter that the next iteration will feel more "interactive" and have a "youthful glow."
"'Idol' will certainly be coming back, for sure," he said.