Parkes has been under growing pressure at the beleaguered Crown safety watchdog.
WorkSafe board chair Jennifer Kerr advised of his resignation.
"Phil has been a strong voice for the need to collectively prioritise health and safety," Kerr said.
"It has been clear to me in interactions I have had, particularly with system partners, that Phil's commitment and passionate and articulate advocacy for health and safety is highly respected."
"Phil has been with WorkSafe for almost nine years and believes the time is right for his next chapter, and for new leadership and thinking for the organisation. I thank him for his service."
WorkSafe had been expected today to announce scores of job cuts.
It has faced widespread criticism over its investigations, with its problems compounded recently by the dismissal of several charges in its landmark Whakaari / White Island prosecutions.
Parkes will continue in the role till the end of 2023.
"It's been a privilege to have worked with such a dedicated team who are committed to reduce work-related harm across Aotearoa. I acknowledge all WorkSafe kaimahi, and our partners in the health and safety system for their commitment to making a difference," he said in a statement.
"Thanks to the organisations and workers who put people first, and the mahi of talented, dedicated people in WorkSafe, we've seen work-related fatalities in Aotearoa reduce since 2013. But there is more to do. We all need to keep doing everything we can to improve health, safety and equitable outcomes across Aotearoa."
