The 31-year-old winger has now added the BBC Wales Sports Personality of the Year Award to his long list of achievements just months away from what is expected to be his second successive tour with the Lions.
The Welsh public voted for Williams ahead of cycling's Olympic gold medalist Nicole Cooke and undisputed world boxing champion Joe Calzaghe, who beat American superstars Bernard Hopkins and Roy Jones Junior in Las Vegas and Madison Square Garden earlier this year.
"It's been crazy over the last 12 months and a dream come true to be honest," said Williams.
"It really is getting better and better and this tops it off. I came here as one of the nominees and I certainly didn't think for one second I was going to win it. Even I voted for Joe Calzaghe."
Williams, who scored five tries for the Lions against Manawatu three years ago was also voted this year's Six Nations Player of the Tournament and has since gone on to take his tally of international tries to 44 in 63 games.
The former Neath player, who went to the 2003 World Cup as third choice scrum-half, was a try scorer on his most-recent outings for both club and country, crossing early on in Wales' defeat of Australia and as a replacement during the Ospreys' win over Treviso last Saturday.