The dual international played a key role in the Roosters' premiership triumph and produced two crucial second half plays in the NRL decider on Sunday that helped the tricolours to an epic come-from-behind-win.
The award capped off an eventful Wednesday for the superstar back-rower when he was earlier included in New Zealand's World Cup squad after initially making himself unavailable for selection.
"I was blessed to come into such a star-studded side," Williams said on receiving the award.
"I've loved playing this season."
Williams' participation in rugby league's end of year showpiece has buoyed the hopes of Roosters and NRL officials who are desperate to keep him in the code in 2014.
He was previously thought to have committed to Super Rugby's Chiefs for next year and beyond but it now appears rugby league may have the front running.
Williams has said he is likely to reach a decision on his future in the next three weeks.
Up and coming winger Daniel Tupou, who scored a spectacular try in the 26-18 grand final win over Manly, was awarded the Roosters' rising star award.
"I didn't think I would get a start at all this year but Robbo (coach Trent Robinson) showed faith in me," Tupou said.
