"I can't say enough about Hayden's efforts," said head coach Dayle Cheatley. "He gave up a career on the road to realise his dream of completing his career back on the track. After eight years away, the sport had moved on and he has worked tirelessly on the bike and been an invaluable leader off it."
The double medallist from Beijing will attend his third Olympics. He takes one of five places in the team pursuit and omnium ranks and is joined by Dylan Kennett, Piet Bulling and Regan Gough, who will make their Games debuts. Aaron Gate, a bronze medallist in the team pursuit at London, completes the quintet.
Roulston pipped Alex Frame and Nick Kergozou for the fifth endurance spot. Williams shaded Matt Archibald and London keirin bronze medallist Simon van Velthooven in the sprinting ranks.
Williams' selection comes as a shock but Cheatley endorsed his talent.
"We have invested significantly in the team sprint and felt it prudent to ensure we have cover. Zac has continued to make significant gains.
"He's been in the elite squads and is not heard of much because the main three sprinters [Ethan Mitchell, Sam Webster and Eddie Dawkins] get the limelight. He's been doing some strong rides across the Olympic nomination period, including a fourth in the keirin at a World Cup which indicate he can be world-class."
The upshot of selecting nine male track riders is that George Bennett is the solitary road cyclist. Commonwealth Games medallist Jack Bauer missed out.
"Jack is an outstanding rider and served us well at London and Glasgow but due to a number of significant injuries and crashes over the last 18 months, we were unable to put his name forward," performance director Mark Elliott said.
"Ultimately we have to make a decision on which team can win the most medals. That's why we've decided to transfer a [men's] road spot to the sprint team so they had cover to carry on their world championship-winning form.
"The key thing for us is to progress from bronzes to silvers and golds."
The women's selections were simpler, with individual time trial world champion Linda Villumsen the main hope for a medal.
Olivia Podmore, a junior world championship medallist, has been added to form a team sprint combination with Natasha Hansen.
The team will continue preparations in Europe before converging on Bordeaux to complete their build-up next week.
NZ Olympic cycling team:
Men's sprint: Eddie Dawkins, Ethan Mitchell, Sam Webster, Zac Williams.
Women's sprint: Natasha Hansen, Olivia Podmore.
Men's endurance: Dylan Kennett, Piet Bulling, Regan Gough, Aaron Gate, Hayden Roulston.
Women's endurance: Rushlee Buchanan, Jaime Nielsen, Racquel Sheath, Lauren Ellis, Georgia Williams.
Men's road: George Bennett.
Women's road: Linda Villumsen.
Men's mountain bike: Sam Gaze.
Men's BMX: Trent Jones.