Worcester returned to the Premiership by coming from 30-16 down on the night to win the Championship play-off final 59-58 on aggregate with two late tries.
After winning 29-28 in the first leg at Ashton Gate, Worcester led 16-6 at half-time with Chris Pennell scoring.
Bristol then looked in control after tries from Jack Lam, Jack Tovey and Matthew Morgan.
But a penalty try and Pennell's effort at the death, converted by Ryan Lamb, made it 30-30 on the night.
It was another stunning contest to match the excitement of the first leg a week earlier, but it was cruel on Andy Robinson's Bristol, who suffered a fourth failure in the play-offs.
|Championship play-off final form guide|
|Worcester lost just three times in 22 games during the Championship season, but two of them were to Bristol - both by just four points.|
|The Warriors made it third time lucky against Bristol, edging the first leg 29-28 at Ashton Gate on 20 May.|
|They also have a better record in the play-offs, having now won twice (they also went up in 2011), in comparison to Bristol's four failures (2010, 2012, 2014 and now 2015).|
Although they matched Worcester on the night, it did not look like it would be that close when the home side opened up an 11-point advantage at half-time thanks to three Lamb penalties and a touchline conversion after full-back Pennell's superb try in the right corner.
The Warriors fly-half put right his kicking failures with the boot at Ashton Gate a week ago. By contrast, this time, it was opposite number Nicky Robinson who was having an off night, missing three of his five first-half penalty attempts on his final appearance.
But Robinson kicked an early second-half penalty. Then, after Cooper Vuna had been sin-binned, Lam, Tovey - only playing because of the first-leg injury to Gavin Henson - and Welsh stand-off Morgan all crossed, with Robinson adding all three conversions.
At 30-16 down, Dean Ryan's Worcester looked spent, but were brought to life by a penalty try and the sin-binnings of Bristol's Lam and Dwayne Peel.
And, up against 13 men, Pennell galloped over again to set up Lamb's conversion which brought Premiership rugby back to Sixways next season.
Worcester Warriors director of rugby Dean Ryan told BBC Hereford & Worcester:
"Sport is cruel. Bristol were the better side on the night. I really do feel for them because that was a game where we escaped - but that has happened to me probably three or four times.
"We really didn't have any of the game in the second half, and the pressure kept coming. When Cooper Vuna went off with a yellow card they had a free run, really.
"Once Cooper was back on, we understood that we needed to get field position and that we could get the forward drive going again.
"We were great last week and we weren't so great in this game, but we got the result. I am a little bit shocked as I never saw that coming, but It has been a long old trawl and today was our day."
Bristol director of rugby Andy Robinson:
"I am hugely disappointed by what has happened. How a player (Dwayne Peel) can get yellow-carded in that last five minutes really infuriates and disappoints me.
"Particularly after what happened in the first half where we had a couple of mauls going over the line when they were illegally stopped.
"These are the small margins of these games. The players were immense, the way they went out and played the game, but it is these small margins that cost and hurt you.
"I can safely say that this is the cruellest bit of sport I have ever been involved in for a team that was outstanding in the way that they played the game. But credit to Worcester for what they did in that last five minutes. They stayed together."
Worcester: Pennell; Biggs, Grove, Mills, Vuna; Lamb, Bruzulier; Rapava Ruskin, Creevy, Schonert, Percival, Thomas, Williams, Betty, van Velze (capt).
Replacements: Annett, Bower, Rees, Senatore, Shillcock, Fatiaki, Howard.
Bristol: Wallace; Amesbury, Tovey, Mosses, Lemi; Robinson, Peel (capt); Traynor, Brooker, Cortes, Glynn, Sorenson, Mama, Lam, Eadie.
Replacements: Crumpton, Perenise, Townson, Robinson, Kessell, Morgan, Maule.