The 32-year-old stopper, who was a free agent after leaving Fiorentina in the summer, agreed terms with the Club after watching part of today's 4-1 win over Aston Villa.
As a free agent, Boruc was able to sign for a team outside of a Transfer Window and Saints will now add him to their Premier League Squad List.
Boruc exclusively told saintsfc.co.uk
: "I'm looking forward to playing in the best league in the world while I'm playing here at Southampton.
"I missed football, so I'm really glad that I'm here and I've finally found the club I was looking for.
"My dreams are coming true," he added of the opportunity to play in England.
"I've been talking about this for a long time, and finally I'm here in the Premier League."
Boruc becomes the third senior goalkeeper at St Mary's, joining Kelvin Davis and Paulo Gazzaniga in battling for the number one jersey.
And the Pole is looking forward to the challenge of getting into Nigel Adkins' starting line-up: "We'll see what's going to happen over the next couple of weeks," he said.
"I'll give 100% and try to get in goal for Southampton. I like challenges and I'm an ambitious guy, so that'll be good for everybody."
First Team Manager Adkins welcomed his new signing, saying: "We're very pleased.
"Artur has great experience from Celtic and Fiorentina, and from playing for the national team in Poland.
"He now gives us a third goalkeeper in the building, which is important because the potential for injuries and people getting sent off means we have to cover ourselves. He gives us great back-up and competition.
"Paulo is a very young goalkeeper and he did ever-so-well for us today, and everyone knows how much I rate Kelvin – what a great character he is and how important he's been in what we've done here at Southampton.
"Artur now comes in as a third goalkeeper with a vast amount of experience."
In Profile: Artur Boruc
Boruc left Serie A giants Fiorentina at the end of last season after two years with the Italians, during which he made 64 appearances.
Previously he spent five campaigns with Glasgow Celtic, playing 186 times and winning the Scottish Premier League three times.
He also picked up the Scottish Cup in 2006-07 as well as the Scottish League Cup in 2005-06 and 2008-09.
Artur made his name in his native Poland with Pogoń Siedice and then Legia Warszawa, where he won the Polish Ekstraklasa in 2001-02 before he joined Celtic – initially on loan – in 2005.
The stopper has notched up 46 caps for his country since making his international debut in 2004.
He was Poland's first-choice stopper at the 2006 FIFA World Cup finals in Germany and UEFA Euro 2008 finals in Austria and Switzerland.
In 2008, Boruc was one of five goalkeepers shortlisted for FIFPro World Player XI awards along with Gianluigi Buffon, Iker Casillas, Petr Cech and Edwin van der Sar.