The 26-year-old was released by the Whites last year following a breach of club discipline, before joining Conference South side Bromley.
Speaking of the signing, manager Karl Robinson told the club's official website: "I met him last night in a service station North of London. He's a player who is very exciting who hopefully can bring us some good fortune.
"He's not played much football, but he has been training with a Championship side. He has been sold for £250,000 in the past. I hope he comes in and can do what he says on the tin. He's top drawer, but his career has taken a little dwindle."
Hall will wear the number 21 shirt.