mexico green jersey Davis, who is currently captaining Northern Ireland at Euro 2016 in France, will now stay at St Mary's until 2019 as a result of his new deal.
USA white jersey The 31-year-old joined Southampton from Rangers in 2012 and scored on his debut in a 3-2 defeat to Manchester City.
He has since made 155 appearances for Saints and netted 11 goals, including five last season.
argentina home shirt Southampton executive director of football Les Reed said: "I am delighted that Steven, another influential leader in the dressing room and on the pitch, has committed his future to Southampton Football Club.
France blue shirt "He is leading Northern Ireland's campaign at Euro 2016 and representing his country and our club as a true ambassador.
England white shirt "Southampton fans know only too well how much energy and effort he puts into games and our players know that when needed he will be there to help them.
spain red jersey "Having coached Steven myself both at club and international level, I know only too well how important he is to whichever team he is playing for."
