Seamer Porter dismissed Richard Levi in the third over of the final morning.
Ryan ten Doeschate (4-31) then took 3-17 from nine overs as Adam Rossington and Azharullah fell lbw and David Murphy was caught at mid-on.
Essex wrapped up victory after lunch as Graham Napier bowled Ben Sanderson as the visitors were all out for 230.
Rory Kleinveldt finished unbeaten on 35, having hit five boundaries, and Richard Gleeson made a career-best 13 but Northants folded against the hosts' pace bowlers.
Porter, who has now claimed 22 wickets at 17.18 from his first three Championship matches of 2016, also picked up a career best of 5-46 in the first innings to help Essex maintain their unbeaten start to the season.
BBC Radio Northampton's Alex Winter: "A pretty poor all-round performance from Northamptonshire here. They bowled waywardly on the first day and have been chasing the game since.
"The batting was marginally better in the second innings but nowhere near good enough to get back in the game.
"Essex have put in an efficient display for a huge win and their second victory of the season. Promotion challenge on?"
Jamie Porter's career-best first-class match figures of 8-91 helped Essex ease to an innings and 92-run victory over Northamptonshire at Chelmsford.