Cohen's new contract will see him at Franklin's Gardens until the end of the 2007/08 season.
Saints chairman Keith Barwell said today: "Ben has been an important part of the club for many years now and I am delighted to confirm he will be staying with us. Ben and I both want to bring silverware to a club that means so much to us, and I hope with his help, that is something we will do in the not too distant future."
Cohen, 26, a member of England's elite playing squad, has earned 45 caps, scored some of the most memorable tries and put in some of the most crucial tackles for his country since his debut against Ireland in 2000. However, he will be trying to put those skills to good use against Glasgow Rugby tomorrow (Fri) night to win Saints a quarter-final place in this season's Heineken Cup.
Cohen, a former Old Scouts RFC player and Kingsthorpe Upper School pupil, said: "I am very happy to have agreed to play for the Saints for at least another three years. I love the club and it feels like home, but that's not the reason I want to stay. I am convinced that this club has the will and the ability to start to win consistently and in the near future compete for every honour available in club rugby. I want to be a part of that, starting tomorrow night against Glasgow."