The 23-year-old insists he will put the effort in at every opportunity in a bid to break into the first-team squad.
He told the club's official website: "It feels brilliant, it's a dream come true, I'm very excited and looking forward to every day in training.
"The manager has put me in with the first-team squad in training so I'm taking that as a positive, I've got to train my hardest and make an impression to get in and around the first team."
Williams has already made an impact at the Madejski Stadium by notching his first goal for the club in a reserve-team game.
He added: "After the reserve game it was quite surreal to say I'd scored for Reading, it was a brilliant feeling and hopefully I can get a few more."