Maarten Stekelenburg has signed a season-long loan agreement with Saints, after Southampton agreed terms with the Dutch goalkeeper's parent club, Fulham.
Stekelenburg, 32, joined the Cottagers in the summer of 2013 and was the club's first-choice goalkeeper until the appointment of Felix Magath.
He subsequently joined Monaco on loan as Fulham looked to get their highest earners off of the wage bill following relegation from the Premier League.
The former Roma goalkeeper was given his debut at Ajax in 2002 at the age of just 19, with his manager at the time being current Saints boss Ronald Koeman.
Stekelenburg made 282 appearances for Ajax, making his debut for the senior Netherlands side in 2004 in a 3-0 win over Liechtenstein.
Following the retirement of Edwin Van der Sar, new Netherlands manager Bert van Marwijk promoted Stekelenburg to become the nation's first-choice goalkeeper.
He starred as the Dutch made it to the 2010 World Cup final in South Africa, conceding just four goals from open play, but walked away with a runners-up medal after an Andres Iniesta goal in the 116th minute clinched victory for Spain.
In 2011 he sealed a move to AS Roma, spending two years in the Italian capital and racking up 55 appearances.
Stekelenburg then moved to the Premier League in June 2013, signing a four-year deal with Fulham.
During his spell in West London he made just 12 appearances, before joining AS Monaco on loan last season.
He becomes Southampton's third addition of the summer, following on from the permanent transfers of Juanmi and Cédric.
"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."
Speaking about the necessity of Stekelenburg's arrival, Executive Director Les Reed highlighted the top-level experience Stekelenburg holds as Saints approach the new season without number one stopper Fraser Forster, due to injury.
"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 stated.
"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."