The 18-year-old made his senior debut in the Capital One Cup clash with Stevenage last season and he has been heavily involved in their pre-season build-up.
Chambers started the games against Schalke and Besiktas and has set his sights on securing a role in the first-team, much as fellow graduates Luke Shaw and James Ward-Prowse did last season.
"It's fantastic - it's like my dream, really," Chambers told the club's website after signing his contract.
"I've been here since I was seven and I've been treated really well so it means the world. The club has a great set-up and it's going through a really good time at the moment. There are going to be big things from Southampton in the future.
"I've always wanted to play for the first team at this club, and this is another step towards that.
"I'd like to push myself into the first team and to prove myself there. I went out [to Spain and Austria] to prove a point because I feel I'm ready, and hopefully I have done that.
"There is a pathway from the Academy for everyone, and hopefully I'm showing that now so I really want to step on."
Boss Mauricio Pochettino added: "Calum has shown in his performances in pre-season that he is more than capable of performing at this level, and we hope that this commitment allows him to push on and thrive within the first team environment.
"He settled into the group nicely during our training camp, demonstrating his maturity off the pitch as well as his quality and potential on it while playing against a good standard of opposition."