The 22-year-old will spend the period with the Hammers' development squad, where he will look to earn a permanent contract.
"I'm very happy to have signed for West Ham," Dixon told the club's official website. "It's a big club with a lot of history. It's good to be here and I'm looking forward to starting.
"I've been to the training ground and I met the manager and some of the players. The manager has got a lot of experience so I'm sure I can learn a lot from him.
"For me it's just about learning and improving as much as I can. I need some time before I'm ready and hopefully it can happen as quickly as possible."
Dixon has recently been playing for non-league Grays Athletic.