The 21-year-old returned to training ahead of Boro`s first pre-season game, versus his former club, Coventry City.
Boro manager Kevin Wilson said: "I'm delighted Billy has signed up for the new season. I've always been aware of his capabilities and I see this a real chance for him to start off on a level playing field and fight for a place in the starting Xl."
Boro face Coventry on Saturday, 9th July at Liberty Way.