After the Folau contract saga with the Catalans Dragons, ending in an eventual release, he lobbied Queensland Rugby League to let him play, which was ultimately agreed to.
He will now turn out alongside his brothers for the remainder of the season for Southport on the Gold Coast, before taking the move to Japan where he has signed a contract to play rugby union.
The contract farce saw Catalans seek a release on compassionate grounds for family reasons.
Southport are said to be hopeful Folau will return to the club and play park rugby league again next season following his stint in Japan.
Williams, who attended Westfields Sports High School together in Sydney with Folau, was on the verge of signing a contract to play in the newly formed United States competition.
However, his deal with the New York Freedom was pulled after he posted on social media in support of Jarryd Hayne after he was sentenced to time in prison.
Williams has 170 games in first grade under his belt, while Folau was a representative player in both rugby league and rugby union.
Folau has been heavily backed by Clive Palmer in his pursuit to return to A Grade rugby league on the Gold Coast.
Southport will host Runaway Bay on Saturday evening.