The former federal treasurer announced his departure on Sunday night after a board meeting on Friday afternoon.

Mr Costello will be succeeded by Catherine West, a former Sky executive in the United Kingdom and Nine’s current deputy chairman.

“After nearly eleven years on the Board of Nine Entertainment Company (NEC) and more than eight years as Chair, I had flagged retiring from the Board some time after the July Olympics and by the AGM in November at latest,’’ Mr Costello said.

“I have today informed the Board of NEC that I will pull forward that timing, stand down as Chair and resign as a Director.

“The Deputy Chair-Catherine West has been working with the Search Firm and is well placed to Chair the company and conclude the process of refreshing the Board.

Mr Costello, who is the father of Nine reporter Seb Costello, said the Board had been “supportive through the events of the last month and last few days in particular.”

“The new Chair will require full support from all Directors as this is an industry where there is fierce rivalry,’’ he said.

“I do not rate the attacks of a commercial rival. The threat to this industry comes externally from Trillion Dollar technology companies that are competing for its business. To stand still or hope to continue to do things as they always have been done is not an option.

“Mr Sneesby has always had my full support as CEO.”

Nine has been engulfed in drama for weeks over revelations that the former news director Darren Wick got a $ 1million retirement payout despite some staff raising concerns about his conduct.

“The Company has set up a robust process to investigate historical complaints which has my full support. I believe it will get to the bottom of any unknown issues,’’ Mr Costello said.

Mr Costello ended with a “note to journalists.”

“I will not be doing any interviews or commenting further on any issues this weekend so no need to maintain vigil outside my home,’’ he complained.

Mr Costello has denied shirt-fronting journalist Liam Mendes and forcing him to fall to the ground during a wild doorstop interview.

Australia’s longest serving Treasurer refused to answer the reporter’s questions on Thursday afternoon and later claimed the reporter came a cropper while walking backwards.

But witnesses have compared the former deputy Liberal leader’s stature to that of “a sumo wrestler” after the 6′ 4″ (1.93m) former MP got up close with reporter Liam Mendes who works for The Australian.

In footage of the incident, he is grilled over the issue in the airport by Mendes, Mr Costello says “Good to see you” to a passer-by before looming large as he advances on the reporter’s camera.

“Don’t, don’t,’’ the reporter says before falling backwards.

The journalist then crashed to the ground, falling backwards with his legs in the air as the camera keeps rolling.

Mr Costello, who is seen standing over Mendes, then turns and walks away as the reporter lies on the ground.

In a statement to the ASX, Nine confirmed Mr Costello had resigned as chairman and will also step down from the Board effective immediately and that Catherine West has been appointed Chair of NEC.

“The Board wishes to thank Mr Costello for his contribution to Nine over more than a decade including eight years as chairman,’’ it said.

“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.”

Ms West said “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.”

2GB’s mornings host Ray Hadley said the Nine chairman had “refused to answer the reporter’s questions relating to the rolling harassment scandal at the company”.

“It’s on the front page of The Sydney Morning Herald which is also an organisation owned in the same interests, he’s rubbished suggestions he should resign,” Hadley told his morning program.

“Look, I’d know what would happen to me if I dropped my shoulder into someone who was trying to interrogate me somewhere, you wouldn’t hear the end of it.

“But from a company’s point of view it’s not really good when the chairman is accused, let alone acted in the way that he allegedly acted.”

Earlier, Opposition Leader Peter Dutton declared that the former Liberal leader doesn’t have “an aggressive bone of that nature in his body”.

Speaking on Channel 9, Mr Dutton said he was “a friend of mine for over 20 years”.

“Firstly, I don’t know Liam, but he’s obviously an excellent journalist,” Mr Dutton said.

“And, the most important thing is that I hope that he’s okay.

“Secondly, to be honest, I’m probably not the best person to ask because Peter’s been a friend of mine for over 20 years, and, I’ve never seen any active aggression from him, there are obviously other camera angles which I haven’t seen.

“But the Peter Costello I know is somebody who doesn’t have an aggressive bone of that nature in his body, and I hope that the matter can be resolved amicably. And, we move on.”

On Sunrise, Education Minister Jason Clare and deputy leader of the Liberal Party Sussan Ley said the details of what had occurred were unclear.

“The journalist said it did happen and Mr Costello said it didn’t happen,” Mr Clare said.

“There is CCTV footage I am sure the airport has. It is a question as to whether they release that or provide it to the police.

The Nine Chairman was in the nation’s capital for the launch of Nine’s newly renovated Canberra bureau in the press gallery.

Mr Costello told reporters at Parliament House that any suggestion he should resign was “rubbish” and he did not “lay a finger” on the reporter.

“As I walked past him, he walked back into an advertising placard and he fell over. I did not strike him. If he’s upset about that, I’m sorry. But I did not strike him,” Mr Costello told Nine newspapers.

“I wasn’t angry. Just like you blokes here if you’re backing back, and there’s a placard behind you, you can walk into it. I’ve seen it happen a million times, I’ve seen it here at Parliament House a million times, reporters back into the bollards and fall over,” he said.

“It’s not assault. As I said before he was backing backwards. He hit an advertising placard. I did not lay a finger or a fist or anything else,” he said.

Speaking on Nine, former treasurer Wayne Swan said that Mr Costello was “no shrinking violet”.

“Well, in public life, you face the blowtorch from time to time and you’ve just got to keep your cool,’’ he said.

“Now there’s an argument about whether he was pushed or shoved or whatever, but, you know, when you’re a senior minister, when you’re the head of a large public company, especially a company which practises quality journalism, you’ve got to be very careful about how you behave.

“But he’s no shrinking violet. He’s given plenty of his time, and you’ve just got to take it.”