New Zealand international Sonny Bill Williams has confirmed he will join Japanese side the Wild Knights for one year after this year's Super 15 competition.

The 26-year-old league convert revealed at a press conference in Hamilton today that he would be leaving the Chiefs in August to take up the lucrative short-term contract in Japan.

He then has a "handshake agreement" to return to the NRL in 2013, although nothing has been signed yet.

Williams said he initially turned down the Japanese attempt to lure him but they came back with an offer he could not refuse.

The dual international, a Rugby World Cup winner last October, accepted the move would likely end his All Blacks career but remained hopeful that would not be the case.

"The decision to come to the Chiefs was a pretty big thing, but it has really helped me, especially off the field," he said. "I didn't think I would love rugby as much as I have.

WIlliams added: "If things work out I would love to come back and play for the All Blacks in the future. But I know there is a group of players who are coming through.

"I've chosen my path now I've got to walk it."