The 31-year-old has scored 13 goals in the Premier League this season, the most of any Englishman, having spearheaded the club's ascent from League One.
Lambert, who first came to St Mary's Stadium in August 2009 from Bristol Rovers for a fee of just £1 million, scored his 100th Saints goal against Newcastle on February 24.
|1/10||Southampton are 1/10 with William Hill to stay up
"There is a lot of ambition in this club for the next few years and that is one of the main reasons that I have signed the contract – and that is why I want to end my career here.
"The core of players who have been together for two or three years are going to be here for another three or four years and that is a really good feeling.
"We all have the same ambition and Nicola [Cortese]'s ambition for this club drives us all on as well, so it really helps the club with where we are now and it will help with where we want to go."