Needing a draw to join Portsmouth, the Rams beat relegated Carlisle thanks to strikes from Max Bird and James Collins.
The result saw Derby ensure Bolton could not climb above them into the automatic promotion places and sparked wild scenes.
Thousands of Rams fans flooded on to the field chanting "we are going up".
It was Derby's second promotion in 26 years and comes after they dropped into League One while in dire financial straits in 2022.
Manager Paul Warne has now led four successful escapes from the third tier - three with former club Rotherham.
He said as cited by Sports Central: "You wake up in the morning and pretend like it is any other game but it isn't. "You have to try to convince the lads to play it like any other game. That's difficult because they are not idiots. "David Clowes brought us in - and I appreciate not the most popular choice - we've come in here to get promoted and we've done it.
He added: "We fell short last year and we wanted to win the title this year. We didn't but we tried to get an average of two points per game which we did. "The lads have been great. And I am really pleased for everybody who works at the football club, the fans and there is no greater fan than the owner. "It's nice when somebody shows you that much respect and belief that you can pay them back. "The highlight for me, and this sounds really saccharine, but when I saw David and his wife Cath, all the heartache and the stress I've taken off my life is worth it."
Bird got derby off to a flier as his curling effort gave them the lead after just five minutes.
And Collins' second-half strike saw the party really start in the stands for a deserving fanbase.
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