Williams, 28, is the first Kiwi to win the award, which has been won by Australian players since its inception in 2008, and it caps a remarkable first year back in the code.
He returned to rugby league with Sydney Roosters at the turn of the year after a five-year absence in rugby union and professional boxing.
The back-rower, along with Huddersfield and Scotland stand-off Brough and South Sydney and Australia full-back Inglis, was selected in the 2013 International Team of the Year, a side selected on performances at club and representative level between October 2012 and November 2013.
The Team of the Year also features England and South Sydney front rower Sam Burgess, the 2013 Prop of the Year who is joined by a third Rabbitoh in Issac Luke, the Hooker of the Year.
The Burgess family had double cause for celebration with George Burgess being named International Rookie of the Year, an award open to players aged 21 or under who made their Test debut during the voting period.