The goalkeeper has committed to Saints until 2016.
"As club captain, Kelvin plays an extremely important role at Southampton," Pochettino said.
"His presence in the dressing room is second to none, and his experience has proved to be vitally important to the club as we look to achieve our aims.
"He has been a massive part of this club during his six and a half years here, and there are few things in football that he hasn't seen so far in his career.
"Every successful team needs to have characters and people like Kelvin, so I'm delighted that he has committed himself to the club for a further three and a half years."