The 24-year-old would take up an 18-month contract with the NZRU, but was yet to decide which provincial and Super 15 teams he would play for, the Sydney Morning Herald reported today.
An official announcement would be made this week.
NZRU acting chief executive Neil Sorensen told media two weeks ago an offer had been made to Williams to play rugby in New Zealand from July.
The offer was "appropriate" for his potential, Reuters reported.
"He's not being offered ridiculous money," Sorenson said.
In April, All Blacks coach Graham Henry advised Williams to return to New Zealand this year to stake his claim for a World Cup spot.
Henry said he'd spoken at length to the gifted former Kiwis league international earlier this year as he mulled over his options before his Toulon contract ended this month.
Williams would take a pay cut if he turned his back on offers from Britain and France, and possibly NRL clubs, to return home to chase a Super 14 contract.
He had walked out on a five-year contract with the Canterbury Bulldogs league side in 2008 to join Toulon.
The French club had recently offered him a world-record $6 million, three-year contract, the Sydney Morning Herald reported.
The NZRU was unable to attempt to match Toulon's offer but had given Williams the choice of which teams he would play for, and he was given the option of returning to Europe or the NRL after the World Cup.
