Schneiderlin will remain at the club until the summer of 2017 after the Saints confirmed they had tied him down to a new deal on Monday evening.
The 24-year-old Frenchman has played an important role for the Saints in their first season back in the top flight, missing just one Premier League match and scoring four goals.
"I am a very happy man," Schneiderlin told Saints Player after completing the seal this evening.
"To commit my future to Southampton is a big thing because this club has big ambitions - and I have big ambitions as well.
"I wouldn't have signed this contract if the club didn't have a big project. When I spoke to the chairman and the manager, I knew they wanted to do something very good at this club and I want to be a part of that.
"My main focus now is to do a great job on the pitch so we achieve all of the ambitions that we have."