Saints set up a mouth-watering derby date with Leicester Tigers at Twickenham after disposing of Saracens 27-13 in the Premiership play-off semi-final at Allianz Park.
Tries from Brian Mujati, Jamie Elliott and GJ van Velze plus 12 points from the boot of the unflappable Stephen Myler secured a memorable triumph.
Saracens were stunned as they fell 17-0 behind inside the first half an hour and they could only respond through replacement Duncan Taylor.
Owen Farrell added eight points with the boot, but there was to be no glory for the regular season table-toppers and 2011 champions.
Instead it will be Saints who march on to Twickenham on May 25 to face their old adversaries in a shoot-out for the Premiership title.
It wasn’t to be a fourth successive play-off semi-final defeat for Jim Mallinder’s men, who defied Elliott’s sin-binning to take the win, to the delight of the big away following.
The victory owed much to the slickest of starts for Saints as they shot out of the blocks to leave Saracens reeling.
The away side put together some scintillating moves and though Myler missed his first two kicks, they were soon on the board.
A typically strong lineout drive saw powerhouse prop Brian Mujati reach over the bodies to touch down.
Myler slotted the extras with aplomb and Saints had their tails up.
They scored again minutes later as human wrecking ball, man of the match, Samu Manoa flew in to help win the ball back. Dylan Hartley broke away and Christian Day gave it to Jamie Elliott, who sprinted over the line.
Myler again converted from out wide and Saints had surged into a 14-0 lead inside the first half hour.
To add to their woes, Saracens were forced to make a change as fly-half Charlie Hodgson, injured early in proceedings, was replaced by Taylor.
Saracens spent the next 10 minutes desperately trying to put the squeeze on Saints and with two minutes to go before the break they finally a chance to grab their first points.
But England man Farrell was surprisingly wide with what looked a simple kick for a player of his calibre.
That miss meant, to the disbelief of most at Allianz Park, Saints held a 17-0 lead at half-time.
They would have known the opening stages of the second half would be crucial, but Saracens emerged with the bit between their teeth and threatened immediately.
David Strettle looked certain to score as he surged towards the line, but some superb work from James Wilson and Ben Foden ensured he was held up on the line.
But Saracens did get on the board soon after as Saints were marched back 10 yards by JP Doyle and Farrell kept his nerve to grab the three points.
The No.12 was on target with another penalty soon after as the home side continued to mount an assault on the Northampton line and chip away at their lead.
But Saints were determined not to buckle and they again broke the Saracens line as Lee Dickson went down the blindside to sent replacement van Velze over in the corner.
Myler again landed a fine conversion from out wide to put his side into a 24-6 lead.
But they were to be hampered by the sin-binning of Elliott seconds after the restart as he misjudged the flight of the ball and took out Chris Ashton.
Saracens took the invitation to get back in the game as they stretched the away backline to its limit and sent Taylor over.
Farrell converted and the home side were back to within 11 points of their opponents.
Saints, with Elliott back in their ranks following his sin-binning, needed a retort and they got one from the boot of Myler, who landed another brilliant effort from out wide.
Northampton had a 14-point lead with eight minutes to go and the vociferous away following were starting to believe.
And they were right to. Saracens had nothing left and Saints were the ones celebrating as the final whistle sounded.
Saracens: Goode; Ashton, Tomkins (Wyles 60), Farrell, Strettle; Hodgson (Taylor 24), de Kock (Wigglesworth 48); Vunipola (Gill 65), Brits (Smit 60), Stevens (Nieto 65); Borthwick, Hargreaves (Botha 71); Brown, Saull (Kruis 48), Wray.
Saints: Foden; K Pisi, Wilson, Burrell (May 69), Elliott; Myler, Dickson (Roberts 69); Tonga’uiha (A Waller 69), Hartley, Mujati (Mercey 65); Lawes (van Velze 46), Day; Clark (Dowson 55), Wood, Manoa.
Replacements not used: Haywood, Lamb.
Referee: JP Doyle