Not only was history against the Saints, but they were also forced to do without England's premier No.9 Matt Dawson, who was stretchered from the field with a knee injury.
Dawson's replacement, Ian Vass, scored a crucial second-half try after a slow start to the game, but a first-half try from Scottish flanker Budge Pountney gave the visitors a handy 13-6 half-time lead.
In the second stanza Northampton were forced to play with 14 men for 10 minutes, when lock Rob Hunter was sin-binned, but a try from centre Chris Hyndman – just over five minutes after Vass's score – gave them enough breathing space to secure a famous win.
Northampton's tenacious defence was the key to their triumph, which sees them leap-frog Leicester on the Zurich Premiership standings. The Tigers are now 13 points behind pace-setters, Gloucester, who have 44 championship points from their 12 matches thus far.
For Leicester:Pens: Stimpson 4
For Northampton:Tries: Pountney, Vass, HyndmanCons: Grayson 2Pens: Grayson 2