The Cherries defender was a key player during last season when Eddie Howe's side recorded their highest ever finish at the club.
Francis told the official club website: "The times I've had here and seeing how far we came last season helped me make my decision.
"I can only see one direction the club is going in and that's up. I think we've got a great chance to continue in that direction, especially this season, and I'm glad to be a part of it."
Francis has made over 100 appearances for the Championship club and has become a regular in the first team since joining from Charlton in 2012.