The 32-year-old will provide cover for Fraser Forster while he recovers from damage to his left patellar tendon he sustained in a win over Burnley in March – the former Celtic goalkeeper has been ruled out for a year.
Stekelenburg joins Saints for the forthcoming season having spent the 2014/15 campaign with AS Monaco where he made just eight appearances for the Champions League quarter-finalists.
He started his career with Ajax, where he made his debut under Southampton manager Ronald Koeman, before spending two years in Italy at AS Roma.
Stekelenburg becomes the Saints third summer signing, following on from last week’s acquisitions of Juanmi and Cédric Soares.
Southampton’s executive director of football of Les Reed revealed there was plenty of competition for Stekelenburg’s signature.
“Maarten is a goalkeeper with a wealth of top-level experience who will prove to be an important addition to the squad at this early stage of pre-season,” Reed told the club’s official website.
“While Fraser Forster’s rehabilitation is progressing well, adding Maarten to our squad alongside Kelvin Davis and Paulo Gazzaniga will give us strength in depth for what will be a busy season.
“Maarten enjoyed tremendous success in Holland with Ajax and on the international stage, playing in the 2010 World Cup final. His experience will be invaluable to us, especially with the arrival of European football.
“There was strong competition for Maarten’s services, so we are very pleased he has committed to our cause.”
Stekelenburg admitted the opportunity to get regular playing time helped him choose Southampton and revealed he is keen to turn his career around after a difficult couple of seasons.
“I’m very pleased that I’ve joined,” Stekelenburg said. “It’s a big, nice club that will play European football – and I can play. Last year I didn’t play a lot, so it’s an opportunity for me. I’m grateful.
”The last two years weren’t the best of my career. As they say in England: the best is yet to come.”