The 34-year-old, a two-time Rugby World Cup victor with New Zealand, has switched codes again having signed a contract reportedly worth 9million Canadian dollars that will make him the highest-paid rugby league player in the world.
He started in league in 2004 with Canterbury Bulldogs, had a stint as a professional heavyweight boxer, and won Rugby World Cups with the All Blacks in 2011 and 2015, as well as NRL titles with the Bulldogs and Sydney Roosters in 2004 and 2013 respectively.
The former Canterbury and Sydney Roosters premiership victor has represented New Zealand in both league and union but is eligible to play for Samoa through his father's heritage.
Williams' signature comes on the back of the Wolfpack's biggest year in the team's very short history, one that saw the Wolfpack achieve their five-year goal of English Super League promotion two years early. "Our city is proud of the success of this team so far and we're ready to keep cheering them on in the Super League".
Wiliams recently met Toronto head coach Brian McDermott for talks during his time with the All Blacks at the rugby union World Cup in Japan.
Just weeks after the New Zealand All Blacks were knocked out of the Rugby World Cup, dual global Sonny Bill Williams will return to rugby league.
Toronto chairman and chief executive Bob Hunter said the acquisition of Williams can raise the profile of rugby league across the globe.
"In our sport, Sonny Bill Williams has been and is that player.We're not going to get the accountants doing the maths on the calculators, but certainly we think there is a commercial value to having a player like this", Pallett said.
The New Zealander will nearly certainly come under the "Marquee Player" rule, which states: 'Each Super League and Championship Club is permitted to have two Marquee Players whose Salary Cap Value is limited to £150,000 (or £75,000 if Club Trained)'.
"Sonny Bill Williams is one of the best rugby players in the world and we welcome him to Toronto". "On the field, I'd like to bring high-quality play and do all I can for the betterment of the team".
"Off the field I'd like to use my experience to mentor the young players and be helpful where I am needed".
"When the Kangaroos tour England in 2020, we will look forward to playing a warm-up game against the Wolfpack as it would create a lot of excitement for the sport".
Williams was part of the New Zealand sevens team that lost in the quarter-finals at the 2016 Rio Olympics.
The Toronto club is reported to have a shopping list of top players which also includes the England rugby union stars Manu Tuilagi and Ben Te'o and Australian league star Valentine Holmes.