Williams is tied to the tiny Puni club, situated over the Pukekohe hill in the Counties Manukau catchment, and previously played one match for Bombay in his return from suspension after the British and Irish Lions series in 2017.
As a contracted Counties player, Williams needed clearance to play for Ponsonby.
Now that has been officially approved by Counties and Auckland - his registration with Ponsonby coming before the last round cut off on July 6th - Williams is available for the Ponies' next two matches.
Williams' presence will be a huge boost for Ponsonby, Gallaher Shield champions, but also Auckland club rugby on the whole.
No doubt there will be additional supporters lining the sidelines, clambering to see the 51-test second five-eighth in action this Saturday, provided he is selected, as Ponsonby takes on Grammar TEC at the Orakei Domain.
Next week could be even more significant, with Williams potentially running out at Western Springs as Ponsonby host Eden.
All Blacks great Sir Bryan Williams, a life-long servant of Ponsonby, will be among those smiling at the prospect. The club is also home to Rieko and Akira Ioane, and has produced the most All Blacks of any at the grassroots.
Playing for Ponsonby over the next two weeks should allow Williams to build conditioning, confidence and fitness as he works towards the All Blacks' first test of the year against the Pumas in Buenos Aires on July 21.
While many believe Williams faces an uphill battle to make the World Cup squad, given the faith the All Blacks retain in him the reality is he probably only needs to regain full fitness to make the plane.