Sonny Bill Williams in 2013.

Former Great Britain coach Brian Noble says there's never been a bigger Super League signing than Sonny Bill Williams' move to the Toronto Wolfpack. 

The Wolfpack announced on Friday morning that Williams will join them on a two-year deal worth up to $10 million.

Noble, Toronto's director of rugby, said the signing eclipses even that of rugby league immortal Andrew Johns who had a stint with Warrington in 2005.

"In my mind unquestionably it's the biggest signing in Super League history, and I've been there from day one in 1996," Noble, the first coach to win three Super League titles, told NRL.com.

"You only need to look at the world news in relation to what we've done and understand it has pretty much been on front pages all around the UK, Europe and North America.

"It's made TV broadcasts and sport shows, so already it's had a huge impact. It's huge for Northern Hemisphere rugby league."

Williams turned 34 recently and will be in his 16th year as a professional sportsman when he takes the field in 2020.

Noble was quick to dismiss any notion that the deal was primarily about using  Williams' profile, arguing that the two-time NRL premiership winner is an even better player than the one who last played league with the Roosters in 2014.

"I think he's much improved since he was last in rugby league and I have no doubt in my mind whatsoever that he will be ready to play a huge part on the field," Noble said.

In my mind unquestionably it's the biggest signing in Super League history

Brian Noble on Sonny Bill Williams

"The humility of the guy will insist that first and foremost he makes an impact on the field.

"The exciting thing for us and SBW is that all of the questions he has asked the football staff and myself are about how can he make the biggest impact on the field, where he needs to be physically and what's expected from the coach.

"Our coach Brian McDermott went out to Japan to meet him during the Rugby World Cup and tell him 'this is my philosophy on football' and I think they agreed on a lot of things, which can only augur well for the type of football he wants to play."

Williams' signing led to a host of players from all over the globe offering their congratulations and support.

Social media was flooded with love for the dual-code superstar with a raft of past and present NRL and Super League stars expressing their excitement.