The 28-year-old Saints Academy graduate has worn the black, green and gold 148 times and has 62 tries to his name, having made his debut in 2004. A try scorer in the 2008 EDF Energy National Trophy final, Diggin has winners' medals for both the Amlin Challenge Cup and LV= Cup, and played for the Saints in the 2011 Heineken Cup final.
However, Diggin was not able to add to his tally of appearances in 2013/14, due to a serious knee injury sustained during a pre-season match against Leinster which ruled him out of the game until the final few weeks of the campaign.
During this enforced absence Diggin helped pass on his knowledge and experience to the next generation, working with the Saints Academy coaching staff to develop the club's age group players.
Although his ambition to represent the Saints remains undimmed, Diggin now also has one eye firmly fixed onto the future, which is why he jumped at the chance to sign this new deal.
"I'm very excited," he said. "It's something that I've always had in the back of my mind. Obviously I've wanted to play on for as long as I could, but opportunities like this don't come along that often and I couldn't turn it down.
"I remain as committed as always to playing for the Saints, and hopefully I will get as much game time as possible this season in what will be a very exciting team. But I've got one eye very much on the future as well and I'm looking forward to working with a group of very talented young players."
Director of rugby Jim Mallinder says that Diggin has the ability to become a talented coach, while still offering a great deal on the playing front, too.
"Paul loves playing for the Saints and representing the town," he said. "And over the past few months it has also been obvious how much he has enjoyed working with the next generation of the club's players.
"It is good to have someone behind the scenes who can instil that appreciation of what it means to play for the club among the younger lads, who has a good understanding of the game, what we're trying to achieve, and who also knows what it takes to graduate from the Saints Academy to become a successful rugby player.
"Paul is at the stage of his career where he is looking to the future, and while we all know how much desire he still has to play for the club he has also made it apparent that he wants to become a coach, and we believe that he has the ability to bring a great deal to our Academy staff."