Josh Stones scored an equaliser 13 minutes into added time that returned York to the Football League – with a dramatic 1-1 draw also featuring an injury-time goal for rivals Rochdale.
Rochdale, needing to win to pip leaders York to the National League title and automatic promotion for themselves at the Crown Oil Arena, scored through Emmanuel Dieseruvwe's header, itself five minutes after the 90.
He rose to convert a cross from veteran Ian Henderson, sparking a pitch invasion from home supporters that delayed the game for six minutes.
Only six minutes added time had been put on the board but, by the time the game restarted, it was the 103rd minute when York striker Stones equalised, with virtually the last kick of the game.
He forced the ball over the line in a terrific scramble after York threw 10 players forward, a goal confirmed after referee Will Finnie consulted his assistant - sparking another pitch invasion, this time by visiting fans.
Rochdale could still go up in the play-offs and might have scored an earlier injury-time goal when York defender Callum Howe headed Casey Pettit's corner against his own crossbar.
But, after recording 108 points to win the league, champions York have completed an impressive comeback, after recently spending five seasons in the sixth-tier National League North.
Stones said: "For the final game to have ended 0-0, it would have been a travesty for the league.
"I'm so happy. We deserve it as a group, the staff, the fans. I love the club and that meant everything.
"I thought it was over, but the boys never say never. If I'm really honest, I hope they [Rochdale] go on and win the playoffs, they've been unbelievable. I missed a chance at 0-0 and I thought if that was it and we lost 1-0, I wouldn't sleep for days. Now I'm not going to sleep for days, in a good way."
The drama in pictures...
Maynard: 'Everything went out of the window... but we kept believing'
"They said it was 'York time'. Before Rochdale scored, it was 'Rochdale time.' There's a real belief and togetherness in this camp," York manager Stuart Maynard told DAZN.
"You've just got to look at the fans behind us. When I first joined, I said we all had to be in this together; the players are warriors.
"When they scored, they're coming over to the dugout and said there's one more chance for us. There's a real belief in us and it kept us going.
"Everything went out the window. Everyone went up front, we had no one back. Kick it, then we get a throw and throw it forward. We know with this group they keep going to the end and they deserve it.
"See all these players behind me, they are incredible. They work so hard, tirelessly every day. We're one big family and I love every single one of them.
"I hope Rochdale go up. It's criminal in this league that teams can get over 100 points and not go up."
