Tries from the outstanding Andrew Trimble and fellow wing Tommy Bowe had put Ulster, runners-up in this competition last year, in command at the interval. Ulster pushed on to seal their 13th consecutive victory of the campaign with a slick try from full-back Jared Payne and Dan Tuohy's last-minute try, which sealed the bonus point.
The Saints have now suffered back-to-back Heineken Cup defeats. Jim Mallinder's men will somehow have to recover from this heavy beating and win at Ravenhill in the return fixture next weekend to stand any chance of reaching the knock-out stages.
Northampton captain, Dylan Hartley, could find himself in hot water with the citing officer after he appeared to strike Ulster hooker Rory Best with a forearm or elbow to the face in an off-the-ball scrap.
Ulster now top Pool Four by six points from Castres with three wins from three. Saints fly-half Ryan Lamb struggled with the boot all night and he missed an early penalty shot at goal before Ulster took control of the game with an excellent try.
Paddy Jackson's clever chip over the top put Ben Foden in trouble and, when he made little ground with the clearance, Ulster drove the lineout within five metres of the Northampton line. Ruan Pienaar swung the ball wide to Jackson, who aimed a perfectly-weighted chip towards the corner and Trimble beat Foden to the touchdown.
Lamb and Jackson both missed penalty shots before the Northampton fly-half finally found his range after a good Saints scrum. Jackson hit back to re-establish Ulster's five-point lead after Roger Wilson, the former Saints number eight, had claimed an acrobatic lineout and Northampton were penalised at the maul.
Northampton were penalised at the five-metre scrum and Ulster turned defence into attack with a brilliant kick to into the corner from Payne. Hartley over-threw the lineout and Ulster punished them. Iain Henderson made two big carries before Pienaar spread play wide right for Bowe to score Ulster's second try on the overlap.
A penalty from Lamb on the stroke of half-time kept the Saints in touch but Darren Cave tore past Callum Clarke and then Trimble through an arrow-like flat pass to Payne, who breezed past Foden to score.
Northampton wing Jamie Elliot was held up over the line by Cave just before Hartley and Best scrapped on the floor, with the England man appearing to twice catch his opposite number in the face. Ulster kept Northampton at bay and the visitors then applied the sucker-punch, scoring with a turnover ball as Payne sent Tuohy over in the corner.