Wycombe reached the Championship for the first time in their 133-year history after beating Oxford 2-1 at Wembley.
Anthony Stewart had given Wanderers an early lead (9) in the League One play-off final on Monday night, only for Mark Sykes to level after the break (57) for Oxford.
Joe Jacobson then stepped up to score a penalty on 79 minutes to fire Gareth Ainsworth's side to promotion, capping a remarkable campaign for a club with one of the lowest budgets in the division.
Oxford, meanwhile, will remain in the League One as their 21-year wait for a return to the second tier continues.
Wycombe end 133-year wait for Championship football
Set-pieces had been so important to Wycombe all season, with Jacobson's left-footed delivery proving pivotal to their success, so there was no surprise to see them take the lead in exactly that fashion after just nine minutes.
The left-back whipped a beauty up to the back stick, where Stewart rose to nod home. There were shades of an own goal about it as it took a big touch off goalkeeper Simon Eastwood on the way through, but it was awarded to the defender.
Oxford were the possession kings of League One, and unsurprisingly dominated throughout the rest of the first half, but rarely caused any problems to the Wycombe defence.
The closest they came was on 36 minutes when Sykes raced into the box and squared it across the six-yard box, but Stewart got back to fire it clear, denying Matty Taylor a tap-in into an open goal.
Sykes would, however, provide the equaliser in stunning fashion after 57 minutes. Whether he meant it or not is another question, as he broke down the right channel and then looped a ball over the helpless Ryan Allsop. It looked like a cross, it may have been a shot, but either way, the Wycombe goalkeeper was caught out completely.
If Allsop had a disappointing moment at one end, then Eastwood had a nightmare at the other to allow Wycombe to get back in front. A complete miscommunication between himself and Elliott Moore at the back allowed Fred Onyedinma in behind, and the Oxford goalkeeper raced to the edge of his box and took him out - leaving the referee with no choice but to point to the spot.
From there, Jacobson stepped up to send Eastwood the wrong way, and send Wycombe into the Championship.
Man of the Match - Anthony Stewart
Two vital moments in the first half. The first - whether it was his strike or an own goal - provided when he rose to head in the opener, the second a vital intervention near his own goal line to keep his side in front. If Oxford had longer to look for a winner, Wycombe may have crumbled under the pressure. Stewart was brilliant for his side.
'Wycombe a wonderful success story'
Paul Warne on Sky Sports:
"Every team that goes up has to improve. They will make changes as well, it will be tough and they'll be underdogs in every game, but they'll enjoy it. There's a lot of work to go in before the start of the Championship, but they've got to enjoy what they've done first."
Darren Moore on Sky Sports:
"[Ainsworth] has been at the club for more than eight years now so he knows every square foot of it, but also the community of the club. It's instrumental that he remains there as they look towards the Championship.
"They need to enjoy this for now and see where it goes from there, but what a wonderful success story. Well done to them all."
What the managers said...
Oxford's Karl Robinson: "We didn't deal with the throw-in that led to the opening goal but from then there was only one team in the game. We were under no pressure whatsoever. In the second half we were very good. I thought we moved the ball efficiently, broke lines, created opportunities.
"We have a lapse in concentration and the rest is history - that's football. Weirdly, that's equally why we love it just as much as we hate it right now. We will take this on the chin; you have to show respect to the opposition. But my players are devastated and I feel for them."
Wycombe's Gareth Ainsworth: "That was just amazing. We can't afford the best footballing players but we've got players with heart and determination and that was a Wycombe performance. I'm so, so proud of the boys. They just ground it out and I still just can't believe that we're a Championship club.
"I think Accrington and maybe Rochdale were down there with us as favourites to go down but we were right down there budget-wise. We had nine players turn up on that first day of pre-season and two of them were trialists. [The owners] Rob and Peter Couhig have come in and they've just enabled me to fill the slots that I had.
"That is for all the fans who are watching at home. I know they were there and we said before the game that we could feel them out on that pitch. That's a good team Karl Robinson has got and now we've beaten both Fleetwood and Oxford, so I think people might start respecting us a little bit more now.
"That win means this club is safe for a few years at least and I feel for so many clubs because COVID-19 has really hurt clubs and I know it's going to be tough for some clubs. But we weren't going to look this opportunity in the mouth, we were going to take it. All my staff have got everyone spot-on for the performances.
"Five years ago, we lost here on penalties but I didn't want lightning to strike twice. I don't even watch Joe Jacobson's penalties normally but I had to watch that one and I'm so glad it's gone in."
Wycombe will begin the 2020/21 campaign in the Championship, while Oxford will remain in League One.