Williams was in Hamilton yesterday with his Chiefs teammates including All Blacks Richard Kahui, Aaron Cruden and Liam Messam, to have their heads shaved to raise money for Leukaemia & Blood Cancer NZ.
He earlier tweeted how he would shave it all off if he did not raise $2000 for cancer and said "trust me u dont wanna see me with a number one".
But after raising the required money, he agreed to go under the clippers anyway.
Hairdresser Lara Witehira said it "would be a bit tragic" to see the rugby star without any hair. She said SBW had created a craze, particularly among young males, with two of his recent hairstyles still popular.
"He had one which was like a comb-over with the sides short whereas the old one was like a mohawk with a box cut - they called it a fro-cut."
"We get a lot of customers coming in to our store wanting a Sonny Bill haircut, actually nearly half our customers want one," she said
Williams said he was happy with his buzz cut look and felt faster because of it.
"I was just telling the boys the last time I had done it was when I was about 10 and it was either keep my long hair with nits in it or shave it off to get in my uncle's pool."
He said the Chiefs, who play the Waratahs in Hamilton on Saturday, were happy to lose their hair for a cause that was close to their hearts.
The Chiefs former team doctor Zig Khouri, who also had his hair shaved off at the fund-raising event yesterday, lost his son Ben to acute lymphoblastic leukaemia last October.
"He lost his son and he was pretty close with all the boys so the boys got behind it this year, and I thought if I had known the bloke I would have done it too," said Williams.
Shave for a Cure is the organisation's biggest annual fundraiser.