The 20-year-old Netherlands youth international would have been a free agent in the summer with the likes of Barcelona, Juventus and Inter Milan all after his signature.
Chong made his debut for the Red Devils in the FA Cup against Reading in January 2019 and has gone on to make 10 appearances for the first team in all competitions this season.
“When I joined Manchester United as a youngster, it was a dream come true,” Chong, who moved to Old Trafford from Feyenoord as a teenager in 2016, said after signing his new contract.
“It is an honour every time I pull on the shirt and represent this club. I am working hard every day to improve and I know this is the perfect environment to develop my game.
“The opportunity to learn from the manager, his coaching staff and the world-class players here is fantastic.
“I am delighted to sign this new contract and really grateful for the chance to prove myself here for many years to come.”
United manager Ole Gunnar Solskjaer added: “Tahith works extremely hard every day and he is constantly improving.
“We are pleased with the progress he has made since he stepped up from the academy and are looking forward to continuing to develop his talent.
“Tahith has great potential; given his age, ability and work ethic, we can see that he has a bright future at Manchester United.”
