"Part of that action must include bringing new leadership that can bring a fresh perspective to the challenges we face and address the issues identified in the Maria Dew report."
Matthews had previously refused to answer questions about his ongoing tenure or his role into an internal probe of a 2019 incident which saw the board and former chief executive criticised sharply by Maria Dew QC.
"I think our statements regarding Maria Dew's report are clear," Matthews wrote in a text message on August 6.
"The board accepts the findings of the report and is committed to support Cam [Wallace] as he addresses the issues raised in the report."
Dew's report highlighted issues current and former staff felt about alleged bullying, the use of drugs at work events, sexist behaviour and harassment and a gender pay gap.
But it also detailed a troubling incident that took place at a promotional event for its commercial radio business in 2019 and the subsequent investigation, of which there was no written record.
Dew's report made it clear that she believed this was a collective failing of senior management responsible for the problems.
"The CEO and ultimately the Board at the time, all had some involvement in the decision making."
Matthews had been chairman of MediaWorks since 2016.
In a statement, the MediaWorks board of directors said it had accepted Matthews' resignation.
"We thank Jack for his work and wish him all the best for the future," the board said in a statement.
The statement said the board was committed to addressing the findings of the Dew review "and ensuring MediaWorks builds a strong culture going forward".
Wayne Stevenson, an existing independent board member, has been named as interim chairman.
Matthews was the founder of one of New Zealand's first cable television services, then known as Saturn. He has previously been chief executive of Showtime in Australia and TelstraSaturn in New Zealand.
He is a director on the board of NZX-listed fibre network company Chorus technology company Plexure.
More to come...