After 43 games, 69 goals and 22 wins, Rotherham United achieved their long-held aim with three matches to spare.
A deserved victory at Gillingham doesn't quite mathematically secure the the fourth-placed Millers qualification for the League One play-offs.
But, as manager Paul Warne said in the build-up to this clash, victory was always going to be enough to all but guarantee a top-six finish.
Rotherham are nine points clear of the team in seventh and can start preparing for an end-of-season assault on the Championship.
Will Vaulks grabbed the all-important goal in the 20th minute and Warne's men passed up on chances after the break to make the margin much greater.
At the final whistle, the players went to the hardy gaggle of 162 away followers in gleeful celebration.
"We deserved to win by more," said Warne. "We missed some excellent chances in the second half."
Rotherham were troubled in the air in their own box in early on, with Gabriel Zakuani, Conor Wilkinson and Connor Ogilvie all heading off target before the match was 11 minutes old.
However, they took the lead in fine style as Josh Emmanuel forced his way to the byline on the right and found Michael Smith whose pull-back to Vaulks was buried hard and low into the bottom corner.
Knowing a win would virtually cement their play-off spot, the Millers were working tirelessly all over the pitch and forced the Gills back with their high-tempo pressing.
Richie Towell saw a shot from distance easily saved before Emmanuel, a big attacking threat throught the opening period, marauded forward yet again on the stroke of half-time and his cross deserved better than a tame finish from the otherwise-impressive Smith.
Rotherham were a long way from home but were up for the challenge in the warm Kent air.
They were the first to show after the break. Centre-half Richard Wood surprised everyone inside the ground, including probably himself, by breaking forward with the ball at his feet for 30 yards before unleashing a 54th-minute 20-yard drive that was tipped for a corner.
Normal service was resumed at the set-piece when Wood threw himself into a header which was blocked.
Williams should have extended the Millers' lead on 67 minutes when he was played through one one one by Vaulks but the winger sent his shot just wide of he post.
The same player missed again five minutes later, this time putting a more difficult chance off target as he tried to head home Jon Taylor's cross.
Smith was the culprit in the 77th minute as Rotherham looked for the goal that would kill the contest, volleying wide of an empty net after Vaulks' pass had set up Taylor for a pinpoint ball in from the right.
Rodak had to saved from Jake Hassenthaler in time added on, but the midfielder's shot was too little to late for the home team who had been well beaten.
43 matches, 69 goals and 22 wins. It's a season of over-achievement already. Three league games left, then a possible three that could complete a remarkable revolution since last term's drop from the second tier.
Gillingham (4-1-3-2): Holy; O'Neill, Ehmer, Zakuani (Nugent 24), Ogilvie (Eaves 52); Byrne; Wagstaff, Hessenthaler, Reilly; Wilkinson, Parker. Subs not used: Hadler, Stevenson, List, Nash, Nasseri.
Rotherham (4-1-4-1): Rodak; Emmanuel, Ihiekwe, Wood, Purrington; Vaulks; Taylor (Forde 78), Towell (Ajayi 65), Palmer, Williams; Smith (Lavery 80). Subs not used: Price, Cummings, Newell, Ball, Lavery.
Goals: Vaulks 20 (Rotherham).
Referee: Dean Whitestone (Northamptonshire)
Attendance: 4,029 (162).