The 27-year-old has linked up with Erik ten Hag's side in the United States, with the Reds currently in the country for Tour 2023.
Andre is no stranger to the boss, with the pair having spent six years together in Amsterdam with Ajax, winning three Eredivisie titles as well as two KNVB Cups.
He also reached the Champions League final with Inter just last season, and will bring a wealth of experience and pedigree to M16.
Onana has been handed the no.24 upon his arrival at Old Trafford and the former Cameroon international follows in the footsteps of Darren Fletcher, Wes Brown, Paul Scholes and David Beckham, who have all worn the shirt previously while with the Reds.