The central defender has underlined his commitment to the club and quashed reports he could be the latest to leave St Mary's, with Hull City and Cardiff City reported to have been monitoring his availability.
Former team-mates Adam Lallana, Rickie Lambert, Luke Shaw, Calum Chambers and Dejan Lovren have all left for Premier League rivals in recent weeks, with Mauricio Pochettino also departing for Tottenham.
However, Fonte has no intention of leaving Southampton and is confident that the south-coast club can have another successful campaign under new manager Ronald Koeman.
"I am very excited to be signing this new contract," said the defender, who has also been installed as captain after penning fresh terms.
"This is where I feel at home, I have been very successful at this club in the last five years.
"It was an easy decision.
"What made me sign was firstly that we signed a very good manager, second the fans and third I believe we have enough quality in the team and with a few strong additions I believe we can have a very strong season, and we will try to do the same as last year or better if we can.
"I can say that everyone in the squad will be working to be better than last year.
"When you see your best mates leave it is hard to see them go, but we have to keep moving forward, this is still a great club."
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