The 32-year-old lock forward is in his second season at Franklin's Gardens, having moved south from Newcastle in the summer of 2010. In that short space of time he has already passed the 50-appearance mark - winning his club cap in the process - and experienced playing in a Heineken Cup final and Aviva Premiership Rugby semi-final.
Born in Wellington, Sorenson moved to England in 2006 from Bay of Plenty, where he had been voted the team's best forward in the Air New Zealand Cup. At Kingston Park he was a firm fans' favourite, winning both the Players' Player and Supporters' Player of the Year awards in 2008.
This season he has featured in all bar two of the Saints' matches in all competitions, helping the team to the LV= Cup semi-finals and scoring his first try in the black, green and gold in December's trip to Castres.
Sorenson had no hesitation in signing again for the Saints.
"I'm excited to have signed again," he said. "Moving to Northampton has been a great move for me, and my family have settled in the area. We've been made to feel very welcome by everyone at the club and the Saints supporters. It's a rugby mad area, which is something I really like and reminds me of where I grew up in New Zealand. The Saints fans are really knowledgeable about their rugby and give us loads of support home and away.
"It's been exciting to have been a part of the club over the past 18 months, especially playing in a massive match like the Heineken Cup final. It's the type of occasion every player wants to be a part of.
"Hopefully we can get something out of the rest of the season. We're in the LV= Cup semi-finals and are well placed in the Aviva Premiership with plenty to build on. And then over the next couple of years we can take the next step up and I'm looking forward to being part of the Saints squad in the future."
Director of rugby Jim Mallinder said he was delighted that Sorenson had signed again.
"Mark has been a good person to have around the club, for both his playing ability and experience," he said. "This is why we signed him in the first place and why we wanted him to stay at Franklin's Gardens. We have plenty of talented youngsters, but you also need some older heads who have experienced the highs and lows in the sport and can set an example for the younger lads."
The Saints also announced that hooker Ross McMillan - who has been on trial at Franklin's Gardens since October - has signed a short-term contract until the end of the season. Brett Sharman has been ruled out for several months after having had an operation following a knee injury sustained in the LV= Cup trip to Bath at the end of January.
