The 25-year-old, who came to New Zealand rugby 12 months ago after playing in the NRL and a stint with French side Toulon, said he had enjoyed his first year back home.
Williams, who played for the Crusaders in this year’s Super Rugby campaign, has not yet confirmed which franchise he will play with next year.
He has been linked to the Chiefs, the Blues and staying with the Crusaders and said he is yet to make his final decision.
The length of the contract means that Williams will have plenty of options open to him for 2013 as he is free to rejoin the NRL after he controversially walked out on the Canterbury-Bankstown Bulldogs in 2008. European union clubs are also likely to be chasing his signature and a switch to boxing fulltime is also a possibility.
However he said he is open to the idea of staying in rugby union in New Zealand longer than a year.