The 27-year-old Williams had been widely expected to join the Roosters for the next National Rugby League season after a short-term contract in Japan, having declined a new agreement with the New Zealand Rugby Union earlier this year.
Williams, who ruptured a pectoral muscle while playing in Japan that could signal the end of the lucrative stint with the Panasonic Wild Knights, said he was fulfilling a long-held promise to play for the Roosters after he sensationally turned his back on rugby league in 2008.
"It was pretty tough (to come back). It's tough, but me and (Roosters chairman) Nick (Politis) are good friends, good mates," Williams said in Sydney.
"He tried to get me when I was an 18-year-old (and) when I made that (handshake) agreement with him I knew it would always be the case (of joining the Roosters when he returned to league)."
Williams sensationally walked away from a long-term contract with the Roosters' cross-town rivals the Canterbury Bulldogs in 2008 to play rugby in France before returning to New Zealand in 2010 in an effort to make the All Blacks 2011 World Cup squad.
He played 19 times for the All Blacks following his debut against England in 2010, though appeared mostly off the bench during the All Blacks' successful World Cup campaign.
The barnstorming inside centre, however, came into his own during the 2012 Super Rugby season, helping the Waikato Chiefs to their first title, and impressing in June internationals against Ireland.
Despite stating he felt he had found his "place" with the Chiefs he declined a new agreement with the NZRU and was photographed in Sydney meeting with Politis.
Williams has also combined professional boxing with his rugby career, but the pectoral injury has forced the postponement of his November 24 bout against South Africa's Francois Botha.
- Sports & Recreation
- New Zealand Rugby Union
- National Rugby League