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?"

Deiseane Santiago, 22, became pregnant in January while visiting her fiancé in Kegworth on a five-month visa.
Her attempt for a UK visa extension was initially denied and the Home Office said she would have to return.
However, the Home Office said it was now reconsidering her case.
On Thursday morning, Miss Santiago was told she was no longer at immediate risk of deportation.
A Home Office statement said: "We are in contact with Ms Santiago and are reconsidering her case."
A friend of the couple, Susan Cooke, said: "It is a great relief that 'Daisy' is no longer at risk of the Home Office turning up on Friday to remove her.
"However, we are not out of the woods yet. But for the first time this week, things are looking hopeful. This could actually turn into a success story with a healthy baby being born in the UK."
Miss Santiago's fiancé, Simon Ellis, said he feels "scared and trapped".
"All I want is a safe birth for my baby," he said.
"I don't want a chance for that baby to catch microcephaly and I don't think I should have to take that chance."
Miss Santiago said: "I'm feeling a lot of stress. I'm depressed, I can't eat.
"If it wasn't about this virus Zika and advice of doctors and my mum telling me that I shouldn't go home, I would be home."
Earlier, supporting an application to extend her visa, her GP cited Public Health England advice over pregnant women travelling to Zika hotspots.
Miss Santiago, from São Paulo, met Mr Ellis online three and a half years ago.
She travelled to Kegworth to visit him in November and the couple got engaged about six weeks ago.
The couple changed her return flight to November - after the baby's due date - and applied to have her visa extended until then.
On Monday, Miss Santiago - now 25 weeks pregnant - was told her application was refused, and that she could be arrested and deported within days.
A letter from the Home Office acknowledged the GP's advice that pregnant women should avoid travel to countries "with active transmission of the Zika virus", but stated advice "is in respect of British nationals travelling to affected countries".
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.
[NEXT_CONCEPT]
A pregnant Brazilian woman advised not to return to the country amid Zika virus fears is to have her UK deportation case reviewed.