The code-hopping Williams had rejoined New Zealand Rugby in 2015 with an eye to making the World Cup squad and then focussing on making the All Blacks Sevens side in an attempt to play at this year's Rio Olympics.
The 30-year-old had joined the side after his World Cup duties and said he had initially struggled with the fitness required, shedding three kilos in the first week of training.
He was named by Gordon Tietjens for his debut in his home tournament in Wellington this weekend.
Williams will be joined by fellow Super Rugby players Ardie Savea, Ben Lam, Augustine Pulu and brothers Rieko and Akira Ioane in the squad, who have struggled with injuries to several of their specialist sevens players on this year's circuit.
The 2013 world champions are seventh on the standings after two rounds of the series and are facing a challenge from emerging nations on this year's circuit, having lost to the United States three times already.
The Wellington tournament is struggling with sluggish ticket sales this year.
While New Zealand have a licence from World Rugby to host a stop on the circuit until 2019, this year's tournament is the last guaranteed to be held in Wellington.
New Zealand Rugby chief executive Steve Tew told local radio over the weekend that only 12,000 tickets had been sold for each day of the tournament, a far cry from less than five years ago when all 35,000 tickets would sell out in minutes.
Wellington has hosted the tournament since 2000.
Last year only about 18,000 people attended each day, down from around 28,000 the previous year, the Dominion Post reported on Monday.
