The 20-year-old was released by Villa this summer after failing to make an appearance and turned down a deal with Ajax after a successful trial.
Bees boss Uwe Rosler told the club's official website: "I'm very happy to have him on board."
Rosler added: "He wanted to explore the possibility of playing for Ajax and he went there, but he's decided to come to us and we are very happy.
"He will fulfil a role that we are lacking. When he is fully fit and learns how we want to play he can be very important for us both now and in the future.
"We will work with him and he can go a long way in the game.
"He is a technical player with good vision and awareness. He will give us goals from midfield."