The Dutch international joins Saints on a season-long loan from Fulham, having spent the 2014/15 campaign with AS Monaco.
He started his career with Ajax, where he made his debut under Ronald Koeman, before spending two years in Italy in AS Roma.
The 32 year-old becomes Saints’ third summer signing, following on from last week’s acquisitions of Juanmi and Cédric.
Executive Director of Football of Les Reed commented: “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.
“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 added: “I’m very pleased that I’ve joined.
“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.”