Williams, who joined the club last term, has decided to keep himself tied down to the Pro12 outfit for a further two years until 2016.
"It's always nice to stay where you're happy," Williams told the club's official website. "My family and I have settled really well and it means I can go out and enjoy myself on the pitch.
"Everything has fallen into place and I wouldn't want to play anywhere else to be honest. We're very excited for this season."
Williams, who won the league's Players' Player of the Season and the IRU PLayers Association Player of the Year award last term, currently sits fifth in the table with his teammates.