"The Board would like to thank Rob for his leadership of Rua. Rob has continued to deliver on the vision of Rua's co-founders, keeping kaupapa and community at the heart of the business."
Mitchell, whose retirement is effective from September 1, said the past two-and-a-half years had been full on at Rua.
He said Rua's social mission had attracted him to the company.
"It has been an honour to work for a company with an explicit mission to benefit its founding community ... and it was a privilege to continue to deliver on the company's kaupapa," Mitchell said.
"I'm proud of the milestones Rua has achieved in recent years, in particular the successful transition from a co-founder-led business to a NZX listed company, developing and launching Rua's first product and establishing New Zealand's first compassionate access programme.
"I remain confident that the commercial success of Rua Bioscience will enable the founding vision to be realised."
Rua director Anna Stove will lead the business as managing director while the Board looks to appoint a new CEO.
Stove joined Rua in 2019 and has a successful track record in leading and driving transformational change within the pharmaceutical sector, the company said.
She has held various senior executive roles within New Zealand, the most recent being NZ general manager of pharmaceutical company GlaxoSmithKline (GSK).
Rua's shares debuted on the NZX at 70c cents, a 20 cent premium to their 50 cent issue price.
A month later its shares had fallen to 52 cents and were trading at 30 cents early this afternoon.
