Williams has established himself as the All Blacks' preferred option at inside centre since switching codes.
He had been expected to move to European club rugby union or make a return to league in Australia's NRL after the World Cup, which takes place in New Zealand in September and October.
But the 25-year-old has now told local media he intends to extend his deal with the NZRU for a further year.
"(My aim was to) make the World Cup squad and then go back off shore and do my trade over there but all the generations from old people to young people and the amount of support I have got has been so humbling," he said.
Williams, however, has not committed himself to remaining with Canterbury Crusaders in the Super Rugby competition.
The Auckland-born player, who excelled in his debut campaign for the beaten-finalist Crusaders, is willing to entertain offers from New Zealand's other franchises.
He also plans to continue his professional boxing career, which has seen him win his first four fights as a heavyweight.
Williams was rested for New Zealand's 60-14 win over Fiji but is expected to be named in the starting XV for their Tri-Nations opener against South Africa on July 30.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
$29.99
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.
