Williams successfully appealed a decision which deemed that a pre-test "game of three halves" hit-out against Counties Manukau and Taranaki did not meet the criteria for a match.
Williams, who was suspended for four weeks for his hit on Lions wing Anthony Watson, had already missed the final Lions test, the Blues loss to the Sunwolves in Tokyo and a Counties Manukau preseason match, meaning he had one more match remaining on his suspension before he could take the field.
The initial ruling meant he could not play until after the Bledisloe opener against Australia on August 19, however, the independent appeal committee, comprising chairman Graeme Mew (Canada) along with Shao-Ing Wang (Singapore) and Stefan Terblanche (South Africa), ruled in favour of Williams after an appeal.
World Rugby released a statement saying the decision 'was surprising' but they won't be stepping in to change it.
"While World Rugby respects the decision of the independent appeal committee to uphold the appeal by New Zealand's Sonny Bill Williams against the matches that counted towards his four-week suspension, it is surprised by the committee's interpretation of the definition of "match" [which is defined in Regulation 1 as 'a game in which two teams compete against each other']," the statement read.
"With the appeal process having been exhausted, World Rugby will refer the interpretation of the regulation to the Regulations Committee when it meets in September to examine the findings in the context of the game's regulations to ensure universal clarity and compliance with the meaning of the regulation moving forward."
A statement by All Blacks coach Steve Hansen helped sway the appeal committee, with the panel writing that Hansen argued that the purpose of the hit-out is to "provide the All Blacks with a more challenging competition by introducing a fresh, but equivalent [in terms of playing level and competitiveness] team in the second period."
The panel noted that the match would have offered Williams a more challenging opportunity, as taking on two competitive opponents for 40 minutes each would have more meaningful consequences than a match against one solitary provincial side.
They also argued that "given the application of normal disciplinary measures and the presence of a citing official, the match will also present the same risks to [Williams] as would any other competitive match."
"We are therefore of the view that the Judicial Committee applied the wrong principles in the exercise of its discretion which resulted in an erroneous decision."
Williams will now serve the final game of his suspension during the "game of three halves" on August 11, and be free to play in the Bledisloe opener on August 19.