The nineteen year old striker left Leeds United over the summer and has spent the past few weeks on trial with the Latics, originally during Owen Coyle's tenure as manager.
New manager Uwe Rosler has moved quickly to secure the signing of the young Australian striker on an eighteen month contract.
Antelmi had originally been offered a two year deal with Leeds but that was just days before Neil Warnock got replaced as manager.
Speaking about the departure from Leeds he said: "It was just unfortunate, it's just one of those things in football. You get hit but you've got to get back up and keep going, that's what I did. I've got something now and I'm happy."
Understandably then Antelmi was nervous about the new manager coming in after his experience in the summer and so was delighted when Rosler asked the striker to sign terms.
"I'm glad that nothing else went wrong after Owen Coyle left and the new manager came in," added Antelmi.
"I'm glad that they still had faith and also I'm guessing the coaches there that stayed obviously had faith in me and passed it on to the new gaffer."
The youngster is a player for the future and has featured for hte development squad during his time with the club.