Georgie Poynton was the toast of Tolka Park as his 74th minute penalty sealed Shelbourne's immediate return to the Premier Division.
It brought redemption at the first time of asking for Ian Morris's side, ending the hurt of last year’s unlikely relegation.
With just one defeat in their 24 games to date, bouncing straight back up with three matches to spare is fully deserved. After the celebrations, the hard work of ensuring they stay up next season will begin in earnest.
It was Shelbourne’s first win of the First Division campaign over a spirited Treaty who stay fourth and well on course to make the play-offs in their debut season in the league.
Unchanged for the fourth successive game, Shelbourne soon grew to dominate possession with the first shot in anger seeing Yassine En-Neyah’s drive blocked by a defender after John Ross Wilson worked hard to carve the opening.
Terrific defending from Stephen Christopher deflected Wilson’s fierce drive out for the first corner of the game on 17 minutes after Shane Farrell had threaded the Shels right-back in on goal.
With the home side maintaining the pressure, Tadhg Ryan came to his side’s rescue with a double save from Ryan Brennan and En-Neyah after Treaty failed to clear Pyonton’s corner.
A weak defensive header then dropped invitingly for Farrell whose first-time volley flashed narrowly wide before Poynton rifled a shot just off target from distance on the half hour.
Ryan remained busy with a comfortable save from Ryan Brennan after an incisive move. He was then well positioned to push Kevin O’Connor’s drive round a post.
Shels continued to knock on the door, defender Ally Gilchrist powering a 38th minute header from Kevin O’Connor’s corner against the back post seven minutes before the interval.
The ball was in the Treaty net from another O’Connor corner minutes later, but the goal was disallowed for a foul on the overworked Ryan.
Though Shels continued to own much of the ball into the second half, they survived a scare on 55 minutes when there was no Treaty player in the area to apply the finish to Marc Ludden’s dangerous low cross.
Brendan Clarke, who had virtually little to do up to that point, then had to produce an outstanding save to keep Treaty out eight minutes later.
Ludden’s low cross was deflected to the well-placed Matt Keane whose powerful drive on the turn was brilliantly tipped over the top by the veteran keeper.
Having survived that drama at their end, it soon arrived at the other to deliver Shelbourne's victory and title.
Clyde O’Connell was a little too touch-tight to Farrell, pulling the Shels player down as he looked to control Kevin O’Connor cross.
Referee Alan Patchell pointed to the spot and, following a delay of a minute or so, including a replacing of the ball on the spot, Poynton emphatically drove the penalty to the net.
Shelbourne: Brendan Clarke; John Ross Wilson, Luke Byrne, Ally Gilchrist, Kameron Ledwidge (Brian McManus 66); Georgie Poynton, Kevin O’Connor; Shane Farrell, Ryan Brennan, Yassine En-Neyah (Dayle Rooney 84); Michael O’Connor
Treaty United: Tadhg Ryan; Charlie Fleming, Mark Walsh, Anthony O’Donnell, Marc Ludden; Callum MaNamara, Clyde O’Connell (Dean George 85); Matt Keane (Joel Coustrain 80), Sean McSweeney (Kieran Hanlon h-t), Stephen Christopher; Conor Melody (William Armshaw 80).
Referee: Alan Patchell (Dublin).