“I’m really happy the club have shown this faith in me.”
Tomori has made 16 appearances for the Blues this season, including a Champions League debut. He also won his first England cap in November, in the match against Kosovo.
Chelsea director Marina Granovskaia said: “We are very happy to see another fantastic young player come through from our academy into the senior team.”
The new deal will keep Tomori at Chelsea until 2024.