The 25 year old has made 37 Gloucester appearances to date, and his fine form in 2012-13 was recognised when he was named as Supporters' Player of the Season.
Capable of playing number eight or at blindside flanker, Kalamafoni has become an integral part of the Gloucester squad, and Director of Rugby Nigel Davies is delighted that another key member of his team has committed to the club.
"It's fantastic news. Sione has attracted attention worldwide, from the likes of Japan and, of course, France.
"He could have made more money elsewhere, but he wants to stay here at Gloucester. He knows the plans that we've put in place and believes in what we're doing. He wants to be part of something here.
"I've said all along that there's a huge commitment here by the board to be successful, and we have clear plans moving forward. Sione and the other recent signings will be a big part of that, and it shows our intent.
"It's great news for Gloucester. He's a fantastic rugby player, versatile enough to play at six, a good lineout option and we all know his work rate around the park. He's got terrific skills and is one of the hardest running eights around."
Kalamafoni himself, currently on international duty with Tonga, explained that extending his stay with Gloucester was an easy decision.
"I'm very happy to have signed a new contract with Gloucester. The club have been great to me, and I am really excited for what the future has to hold for the squad and myself.
"I love the atmosphere at Kingsholm and how the fans get behind the players. When they chose me as their Player of the Season, it was a very proud moment.
"For now though, I am looking forward to getting back and working hard, so that the team plays as well as possible for the rest of the season.
"I'd like to thank the coaches and my team mates for helping my development as a player, and for helping me make the step up from the Championship.
"I am also grateful to God for the talent he has given me and how he has blessed my family and myself. If it weren't for him, I wouldn't have this opportunity to play rugby in England.
"Finally, I am thankful for all the prayers and support from my family, especially my wife. They have inspired me to get this far."