After four years in the wilderness Millwall will finally grace the Championship once more as Paul Robinson proved the hero again as his goal earned The Lions a thoroughly deserved victory.
Millwall had several chances but Robins keeper David Lucas was in inspired form to keep out Neil Harris early then deny Steve Morison after The Lions striker's driving run.
But it was Robinson who would be the one to score the goal that finally ended Millwall'd four year exile, with Charlie Austin spurning a glorious opportunity to level, only to fire wide with just Forde to beat.
Injury to Jack Smith meant Scott Barron was drafted in as an emergeancy right-back with Tony Craig taking the opposite flank.
Robinson and Darren Ward filled the centre half places, whilst ahead of them, Liam Trotter and Jimmy Abdou formed the midfield engine room with Danny Schofield on the left and Shaun Batt on the right.
Up front, Steve Morison and Neil Harris had the chance to continue their fine partnership.
Backed by a wall of noise from the 37,000 Lions fans packed into the Millwall end, it was the men in blue who kicked off.
The Lions fashioned the first real chance. Craig's ball down the line found Harris who shimmied this way and that before creating the angle he wanted. However his curling shot was palmed over by Robins keeper Lucas.
Swindon's number one then needed a dose of luck to race off his line and clear away a dangerously loose ball from under the nose of a lurking Morison as Millwall looked to take the game by the scruff of the neck.
The Lions were growing in confidence as the half wore on, Schofield's neat through ball set up Morison and his delightful chip looked to be sailing over the head of Lucas into the net but the flight just took it over the bar.
Schofield then got in on the act himself drilling a shot wide from inside the box.
Another well crafted attack involving Abdou, Schofield and Morison teed up Harris but he scuffed his 20-yard shot and it failed to trouble Lucas.
Swindon looked to recover from the barrage but even when they had the ball in Millwall's half, The Lions were looking sharp on the counter, Abdou's clever bit of skill allowed him to find Batt on the right who cut in on his weaker left foot and as such, his effort lacked power.
Sheehan then saw his long range free-kick evade Lescinel Jean-Francois and then the upright as The Robins hit back, Austin crashing another ranged effort high and wide.
Then, controversy, but ultimately a correct decision. Harris freed Batt on the right and his pinpoint cross flew in off the head of Amankwaah, only for the linesman to flag his intended target Trotter offside.
It proved a wake up call for Swindon and Sheehan duly delivered a reminder that Millwall were not the only team at Wembley. His run and shot from 25-yards had Forde worried enough to force the Irishman to dive to his right but in the end it fizzed narrowly over.
But The Lions refused to let The Robins back into it and pressed forward again. Barron's free-kick was cleverly chested into Morison's path by Harris but Scott Cuthbert did very well to throw is body in the way. The rebound found it's way to Craig, whose speculative drive from out wide on the left flew harmlessly wide.
A succession of corners then led to the breakthrough. And it was captain Robinson to lead by example with a well taken opener. Schofield's whipped in delivery from the left flicked off the head of Cuthbert and bounced off the skipper who then swivelled to poke the ball home from four yards out, prompting a barrage of noise from the Millwall end that lifted the roof off Wembley.
The Lions came inches away from doubling their lead when Morison's neat flick played in Harris but Jean-Francois and then Lucas did well to clear the danger.
Shortly after Morison's determined run from the right nearly found a way through but Swindon had enough bodies in the way.
Millwall were then dealt a cruel blow as they lost left-back Craig, who was helped off with a foot injury. On came Andy Frampton in a direct swap.
Town emerged from the tunnel in determined fashion and set about trying to overturn the deficit from the outset at the start of the second half.
Several over-hit through balls from Simon Ferry and Jonathan Douglas just needed a bit more luck to open up The Lions defence as Millwall started the half on the back foot. But suddenly Batt was put through by Morison's alert pass and it seemed like the pacey striker was on goal. But twice came Cuthbert to brilliantly dive in and nick the ball away before he could race clear. Swindon were clearly up for it after Danny Wilson's teamtalk and a collection of Schofield and Robinson bravely dived at the feet of Danny Ward to stop the on-loan Bolton forward from firing in on goal.
Cuthbert was at it again seconds later, staying with Morison as he bore down on goal following Trotter's superb pass, and getting the block in as the former Stevenage man shaped to shoot.
From the resultant corner, Morison's header was going wide even when cleared. Suddenly it was Millwall on the front foot, with good build up play from Schofield and Harris saw the latter sting the palms of Lucas, then Morison's follow up again blocked by Cuthbert.
The game was opening up nicely, and Austin was unlucky with a shot on the turn, Robinson doing just enough to get a touch on it to send it high and wide. Then from a Jon-Paul McGovern corner, Jean-Francois's powerful header was comfortably dealt with by Forde.
The Lions custodian was again called into action and again he excelled, rising high to claim a McGovern centre under pressure from two Robins.
Up the other end, Millwall had a great chance to add another goal but Morison could only guide his left-foot shot straight at Lucas after doing superbly well to burst past two Swindon defenders.
Cramp to Batt allowed Town to make a change in a bid to turn the tide, Stephen Darby replacing Sheehan. In quick succession, Kenny Jackett played his second card, replacing Batt with Chris Hackett.
Millwall, quite devoid of luck in their Play-Off history saw a huge change in their fortunes on 70 minutes as Austin was guilty of a game-turning miss. An error from Robinson of all people let in the former non-league man and as he raced through on goal, most of the packed out Wembley thought it was 1-1. Thankfully he failed to hit the target with only Forde to beat.
Shaken, The Lions looked to pick up the pace, but Morison could only blaze a long range drive from out wide on the right over the bar. Then Trotter got lucky in the middle and set off towards the Swindon goal, playing in Harris on the left. As he approached the area, Millwall's talisman cut inside but his curling strike flew around the post inside of inside it.
Some excellent work from Morison allowed him space to shoot but he chose the wrong option and tried to place it with his right instead of drilling it with his left.
A foul on The Lions top scorer gave Millwall a free-kick and Barron's deep delivery saw Robinson challenge Lucas and send a header that looked to be going in, but there was Cuthbert once again to acrobatically hook it off the line.
With time running out, clever build up play found Swindon's Ward on the right but his effort flew wide to the relief of half the ground. Then Forde needed all of his considerable frame to palm a deflected Austin shot around the post.
It proved decisive as seconds later, half of Wembley erupted in an explosion of noise and blue. Millwall had done it. At long last.

Millwall: Forde, Barron, Craig (Frampton, 43mins), Abdou, Robinson, Ward, Trotter, Schofield, Harris, Morison, Batt (Hackett, 69mins). Subs not used: Sullivan, Laird, Fuseini, Alexander, Obika.
Scorer: Robinson (39mins)

Swindon Town: Lucas, Cuthbert, Sheehan (Darby, 66mins), Douglas, McGovern (O'Brien, 72mins), Amankwaah, Jean-Francois, Paynter (Pericard, 81mins), Ward, Ferry, Austin. Subs not used: Smith, Easton, Timlin, Morrisson.

Ref: Colin Webster
Att: 73,108