The Poland international's contract was set to expire in June but he has agreed terms over an extension.
The former Celtic keeper, 33, has started Southampton's last 15 games - only four of which have ended in defeat.
"I am very pleased and I'm proud to be a part of a big project," he told the club's official website. "As a club, I believe we can achieve a lot over the next two years, and I'm looking forward to that.
"The Premier League is probably the best place to play football and nothing has changed my mind on that since I came to Southampton.
"The new manager has changed a lot - we're playing totally different football, and I think that football is quite nice to watch and quite effective."
Manager Mauricio Pochettino added: "I'm very happy and very satisfied. Artur deserves this contract because, in the three months that I've been here, he has been crucial for us.
"He has a very strong personalty and character. He is very brave in the way that he plays and, with our brand of football, it's very important that we have a 'keeper like Boruc for the long term."