All Blacks coach Steve Hansen has predicted Sonny Bill Williams will finish as a rugby union great as he sets his sights on a record third consecutive Rugby World Cup triumph with New Zealand.

Dual international Williams, 30, ended speculation about possible moves to European rugby or back to the NRL on Wednesday by recommitting to New Zealand Rugby until the end of the 2019 World Cup year.

He said he actually made the decision to stay — and to change his usual practice of signing one-year deals — soon after playing in New Zealand's World Cup triumph in Britain last year, when Hansen rang him.

He is now one of a very small group of All Blacks including new captain Kieran Read who are in the mix to chase a third straight World Cup title, having also played in the 2011 home World Cup win.