The 25-year-old defender, who has also played in midfield in spells of his career, joins the Eagles until the end of the 2024/25 season.
Having been with the Blues since the age of nine, Chalobah’s first taste of senior football came in the form of three successful seasons on loan at Ipswich Town and Huddersfield Town (in the Championship) and Lorient (in Ligue 1).
He subsequently broke through into the Chelsea first-team squad at the start of the 2021/22 season, lifting silverware in his very first appearance: the 2021 UEFA Super Cup win over Villarreal.
Chalobah has gone on to make 80 appearances for Chelsea over the last three seasons, scoring five times, including against Juventus in the UEFA Champions League. He has also represented England Under-21s on three occasions.
He becomes Palace’s seventh signing of the summer, following the arrivals of Chadi Riad, Daichi Kamada, Ismaila Sarr, Maxence Lacroix, Eddie Nketiah and Matt Turner.
Chalobah said: “I'm delighted to join an ambitious club like Crystal Palace. I know some of the boys in the squad well and I'm looking forward to playing alongside them in front of the amazing support at Selhurst Park.”
Chairman Steve Parish also said: “Trevoh is a talented young man and when the opportunity to bring him to Palace for the season arose, we were determined to seize it. I’m delighted that he has joined us on loan, and we believe he will be a great addition.”