Peter Costello has resigned from his position as chairman of Nine Entertainment and will immediately step down from the media company's board following intense media scrutiny that last week culminated in allegations that he assaulted a reporter at Canberra Airport on Thursday.

The media executive and former Australian treasurer, who has been on the media company's board since 2013, will be replaced as chair by Catherine West, who has more than three decades of media and entertainment experience across the UK, Europe and Australia. Her appointment is part of a broader reshuffle, with Mickie Rosen joining the Audit & Risk Committee and Mandy Pattinson becoming the Chair of the People & Remuneration Committee.

"On behalf of the Board I want to thank Peter for his dedication and commitment to Nine. Peter has led the transformation of Nine from a free to air network to a fully integrated media company with traditional and digital media assets across television, streaming publishing, audio and marketplaces. As Chairman, he has always put the needs of the company first and his decision to stand down and pass on the baton of leading Nine at this time is in line with that approach," said West.

Costello's tenure at Nine saw several key milestones, including the company's successful re-listing on the Australian Stock Exchange in 2013, the securing of the landmark News Media Bargaining Code, and the transformative merger with Fairfax Media. His resignation comes amidst a broader renewal and succession plan initiated by the Board last year, which involved a search firm identifying potential new directors.

"I thank the Board for their support over the last decade and particularly during the events of the last few weeks. I wish the Board, the employees and the Company well. There are enormous challenges ahead but I believe Nine is the best placed Australian media company to weather them and prosper," said Costello.

Nine indicated that the Board and management will now focus on the well-being of their people across all parts of the business, acknowledging the recent events have been extremely destabilising for employees and other stakeholders.

"The Board knows that the events of recent weeks have been extremely difficult and de-stabilising for our employees and other stakeholders and we are committed to ensuring, through our cultural review and other actions announced last week, that issues will be appropriately addressed," West said. "The Board and management are united in focusing on the well-being of our people in all parts of our business. At Nine, we do work that has an important value to the community and the Board and management acknowledge their responsibility to ensure all parts of business, including our newsrooms, feel supported. We want to ensure our people can feel proud of our company and colleagues and the work they do."

Costello's exit has been welcomed by Nine masthead The Sydney Morning Herald, which in an editorial published online on Monday said "everyone with half a grip on reality knew Peter Costello’s tenure as Nine Entertainment chair was over the moment footage emerged of the former federal treasurer dropping his shoulder and barging into a reporter at Canberra".

The incident, which was recorded on camera, saw Costello allegedly knock down a reporter from The Australian as he was being questioned over sexual harassment issues within Nine's newsrooms.

Those issues have been the subject of widespread media scrutiny over recent week's with Costello and Nine Entertainment chief Mike Sneesby facing mounting pressure to answer up to allegations of abuses of power and “drunken, lecherous behaviour” within its newsrooms.

Following a report by the Sydney Morning Herald about sexual harassment allegations surrounding Darren Wick, the now former director of news and current affairs, Nine moved to launch an external review of its newsroom culture.