David Ripley's men are now right in the mix for a top two finish that would see them compete for the Championship title in the play-offs at the end of the season.
The County's third win of the campaign, and second over Sussex, was secured with the minimum of fuss.
Resuming on 131 for two, still needing 87 runs to win, Northants did lose an early wicket when Luke Procter was dismissed for a well-made 51, but they eased home thanks to unbeaten knocks from in-form pair Rob Keogh and Saif Zaib
Keogh played the anchor role to finish on 60 not out from 112 balls, while Zaib's breezy unbeaten 47 from just 43 balls got the job done in quick time, with only 65 minutes of play needed..
At the start of play on the last day the main question was whether the match would survive until lunch - and it didn't.
The odds were always against a young and inexperienced Sussex side, particularly on a pitch that appeared to flatten out as the match progressed.
And batting conditions were never more benign than on the fourth morning, when there was hardly a cloud in the sky.
Sussex opened up with Delray Rawlins’ left-arm spin from the sea end and the bouncy pace of Jamie Atkins.
Procter reached his 50 when he worked Rawlins through midwicket for two, and he had faced 149 balls and hit five fours.
But he had added just one run to his score when he was out, flailing at a wide delivery from Atkins for Aaron Thomason to take a good catch low down at first slip.
The Sussex team celebrated, but it was to be their only breakthrough of a short day.
The game ended with a flurry of blows, mostly from Zaib, who showed his intentions when he took a step down the wicket and clouted Rawlins over wide mid-on for six.
Northants moved up to third, and to within a point of second-placed Yorkshire, who face an uphill battle to secure a draw against Lancashire at Old Trafford on Sunday.
The County are back in action on Thursday when the travel to Canterbury to play bottom-of-the-table Kent.