With Walter Smith’s men down to nine men following the dismissals of Kevin Thomson and Danny Wilson St. Mirren looked favourites to go on to win this epic battle.
But with time running out substitute Steven Naismith darted down the right wing and his pinpoint cross was met by Miller who powered his effort past the helpless Paul Gallacher.
The Rangers fans went wild and no wonder – this team has a fighting spirit that has rarely been matched and this victory tested their resolve to the limit.
Neil Alexander lined up in goal as Walter Smith made just one change to his team that faced Dundee United last weekend.
The keeper replaced Allan McGregor and with Madjid Bougherra again ruled out through injury he lined up behind the same back four that faced the Terrors seven days ago.
That meant a first major cup final for Wilson who partnered David Weir at the heart of the defence with Steven Whittaker and Sasa Papac taking their usual spots on the flanks.
In front of them Steven Davis continued on the right despite being a late doubt due to illness with Nacho Novo on the opposite wing.
Lee McCulloch joined Thomson in the heart of the engine room before McCulloch’s suspension kicks in this midweek at Tannadice.
Up front, 40-goal pair Kenny Miller and Kris Boyd were given the task of finding the goals to clinch the season’s first piece of silverware.
The atmosphere was electric at kick-off with Rangers fans holding up cards to display a stunning Union Jack while the Saints fans were clearly out to enjoy their trip to the national stadium.
And it was the Paisley side that started the brighter of the two sides with Rangers pegged back in the early stages.
On four minutes a slip from Davie Weir on the Main Stand side of the pitch allowed Billy Mehmet to sprint clear down the right and his cross spun off Danny Wilson’s foot and over Alexander.
Fortunately Sasa Papac got in front of Hugh Murray and headed the ball out for a corner.
Before the game Smith warned his side that this was going to be a battle and the opening 15 minutes of this contest highlighted this fact with the Saints players throwing themselves in to every challenge and defending deep when Rangers had possession.
Indeed, Lee McCulloch felt the full force of a late challenge from Murray which left the Scotland midfielder in some pain on the turf and gave referee Craig Thomson no option but to issue the first yellow card of the game.
On 22 minutes Gallacher was called in to action for the first time when Whittaker tried his luck with a speculative 30 yard shot which skimmed off the grass but went safely in to the hands of the keeper.
But at this stage this was as good as it got for the Light Blues who were sloppy going forward and struggling to get men up the park to support Miller and the isolated Boyd.
Before the half-hour mark the Buddies were gifted the perfect opportunity to push forward when a mix-up between Wilson and Weir allowed Mehmet to send Thomson clear on the right.
Fortunately his cross was too long but when the ball was collected by Graham Carey Steven Whittaker was booked for what appeared to be a fair challenge on the left-back.
The lack of quality coming from Rangers was proving a real concern for the Gers coaching staff with Walter Smith seen scratching his head with frustration at the space of time St. Mirren were being given on the ball.
On 34 minutes, however, Miller showed his quality when he cut in from the right and when he skipped past John Potter the goal opened up but his effort went well over the bar.
At the other end Alexander saved the day for Rangers with an outstanding stop.
Hidgon jigged past Weir to get to the byline and his cut back found Murray who blasted a shot goalwards.
Alexander, however, showed great agility to get back across and make a stunning save with his legs.
From the resulting corner McCulloch headed the ball away but when it arrived at feet of David Barron his terrific 30 yard drive clipped the cross bar with Alexander beaten.
With the clock ticking down Higdon, who was hugely effective in the first half, latched on to a Mehmet flick-on and the Gers’ keeper looked relieved to see his shot ripple the side netting at his near post.
The only positive for Rangers at half-time was that they were not behind and the speed in which Walter Smith and Ally McCoist darted down the tunnel suggested that a few harsh words must have been said at the break.
Mo Edu swapped with Steven Davis for the restart with the Northern Ireland man clearly not at his brilliant best due to illness.
And Rangers immediately looked sharper with Novo winning a free-kick in a dangerous area down the right.
The Spaniard drilled the result free-kick in to the box and when it was partially cleared Kevin Thomson skewed a 20-yard shot wide of target.
At the other end the Saints continued to be a threat and when Higdon headed a Murray pass across goal Memhet’s turn and shot trickled in to the arms of Alexander.
If the striker had got any power on the shot whatsoever the ball would have finished in the net.
With 53 minutes of the game played the final was turned on its head with the controversial sending off of Kevin Thomson.
The midfielder produced one of his trademark crunching challenges on his namesake Steven Thomson.
It was a yellow card but not a red and this decision was to ignite what was becoming a volatile encounter.
But with Rangers down to ten men they started to enjoy their best period of the match with Boyd coming close with a header from a Nacho Novo free-kick.
Edu’s athleticism was making a difference and when the American won a free-kick down the right Novo’s cross caused havoc before Miller’s close-range shot was deflected out for another corner.
With 71 minutes played this game took another twist in St. Mirren favour when Wilson was shown a straight red card for a last ditch challenge on Dargo.
The Saints’ sub got goal side of the 18-year-old who was adjudged to have brought the striker to the turf.
This was now starting to look like mission impossible for the Gers who would need a miracle to keep their cup dreams alive.
With just over ten minutes left Kris Boyd was taken off and replaced by Naismith who was asked to play in the middle of the park with Miller now a lone striker as part of a 4-3-1 formation.
But this is as resilient a Rangers team as you are ever likely to see and on 84 minutes the Hampden roof was taken off when Rangers got their noses in front.
Despite being two men down they found themselves in a 3 v 2 situation and when Naismith curled in a delightful cross Miller was there to power a fantastic header in to the net.
Despite an agonising final ten minutes, which seemed to last an hour, the brave men in blue held out for what will surely go down as one of their greatest cup victories.