The 16-year-old Frenchman, who began his career with the Stamford Bridge club, signed his form at United’s Carrington training ground on Sunday.
He did so alongside a number of other academy recruits, including the highly-rated French youngster Aliou Traore from Paris Saint-Germain.
Bernard responded enthusiastically after putting pen to paper with the Red Devils, taking to Twitter to write: “My new chapter begins.”
He later re-tweeted a post from a Danish Premier League journalist, which read: “Chelsea will regret this big time!”
Man United’s Under-18 coach Kieran McKenna will have his hands full with no fewer than nine youngsters joining the academy ahead of next season.
Belgian teenager Largie Ramazani is another star who has recently moved to United on a scholarship contract from League One side Charlton.
According to the Manchester Evening News, United arranged for club favourite Andy Cole to greet the teenagers as they signed their forms.
The ex-Red Devils forward posed with the prospects alongside their new boss McKenna at the Carrington training ground.