The striker's third goal of the campaign moves the Reds up to 11th, just four points off the play-offs, and maintains Crawley's 100 per cent winning record in 2022.
The Cobblers, meanwhile, have fallen to third and remain eight points behind leaders Forest Green Rovers.
Manager John Yems was forced into two changes from their last outing against Colchester United on New Year's Day. Injuries to Will Ferry and Kwesi Appiah meant they missed out, with Nick Tsaroulla and Sam Matthews taking their place.
The visitors forged their first chance of the game inside five minutes. Matthews laid the ball off for Jame Tilley, who cut inside and fired an effort just over the bar from outside the area.
Crawley thought they had taken the lead midway through the first half. Matthews coolly fired past Cobblers stopper Liam Roberts after a brilliant pass by Tsaroulla but the linesman had his flag up for offside.
But the Reds were not to be denied four minutes before half-time. Nichols judged his run expertly to beat the offside trap and thump to ball home.
After a quiet opening to the second half, the hosts ramped up the pressure in the final 15 minutes.
Aaron McGowan drilled a ball into the box from a set-piece and substitute Chanka Zimba cracked the crossbar from close-range.
Fraser Horsfall's header from a corner looked destined to hit the back of the net but the effort was kept out and cleared only as far as McGowan.
The Northampton left back composed himself and unleashed a well hit shot that flashed just wide.
And with two minutes remaining Glenn Morris made a superb save to preserve Crawley's lead. Zimba was put through one-on-one with Morris but the Reds keeper did excellently to deny a certain goal and direct the ball behind for a corner.
Crawley Town: Morris, Francillette, Craig, Lynch, Tilley, Francomb, Powell, Tsaroulla (Davies 62), Matthews (Payne 53), Nadesan (Ashford 83), Nichols. Unused: Seymour, Marshall, Kastrati.