Williams, 25, who previously played for Harlequins, stands at 6ft 7in and helped lead the Skolars to the brink of the Championship 1 play-offs last season.
Head Coach Joe Mbu said: “It’s a great boost to the 2013 campaign for us. He’s going to give us that strength in depth that we’ve lacked in the past.
“He was a very important player for us. He’s consistent, takes the ball up well and makes the tackles. I believe his work rate goes unnoticed. The one game he didn’t play you could clearly see there was a big hole where he usually is.”
Williams said: “I’m really happy to have signed so we can carry on what we started last year. I had a really good time, it’s good to be playing week in week out . Working with Joe and everyone was really good.
“It will be interesting next year, with the three new teams coming in, seeing how they adapt to this level and also how the Welsh teams kick on. I think if we can keep most of the team we had last year together we should be right up there with a good chance of winning the thing. That’s why I’ve signed again, that’s what I think we can do.”