The defender, who joined the club at the age of nine and has progressed through the ranks to become a regular in the senior side, is now committed to the Blues until at least June 2028, with a club option to extend to 2029.
A Cobham graduate who followed his older brother Nathaniel in becoming a professional footballer, Chalobah has made 13 appearances so far this season in all competitions.
Chelsea chairman Todd Boehly and co-controlling owner Behdad Eghbali said: "We're delighted that Trevoh will be extending his stay with Chelsea. He has been with us since childhood and has grown into an exceptional young player. He's an important part of our men's first team squad and we're excited to see what's next for Trevoh at Chelsea."
On signing his new deal, Chalobah said: "I'm over the moon to sign this contract. It's been an honour every time I put the shirt on. I want to give my all and do anything for this club.
"As everyone knows I've been here from a young age and to continue here is every kid's dream. Whenever I get the chance, I'll give my all for the club and look for the future ahead.
"I want to say thanks to God for this, without Him none of this would be possible. And just always believing. Thanks to my family as well and the club for trusting in me. I'll now continue to give my all."