The 16-year-old signed a contract with the Red Devils in July but had his transfer held up because of international clearing.
And while United have not yet confirmed the deal, the starlet shared a picture of himself with club legend Andy Cole and Under-18 coach Kieran McKenna on his social channel.
Puigmal announced: "Very happy and proud to announce that I am a new Manchester United player, a dream come true. It's time to work, come on Red Devils!"
Puigmal, a central midfielder, was named most valuable player at the most recent Mediterranean International Cup, a tournament in which Lionel Messi previously competed in.