John Campbell will leave Campbell Live, with a new current affairs show continuing in his time slot four days a week, with two presenters.
Campbell has rejected the chance to co-host a revamped version of his television show and quit MediaWorks, the company says.
According to the 3News website, group head of news Mark Jennings said Campbell was asked to co-host the show, which will have two presenters, but decided to leave the company.
"John has decided he wants to take a break from the job and we respect his decision," Jennings said.
The announcement ended a six-week review of this show.
MediaWorks chief executive Mark Weldon and Jennings told staff today, 3News reported.
Two security guards are patrolling the premises and media have been told to stay out.
It is believed staff have been given a directive not to speak to media.
Multiple taxis have been spotted ferrying staff away from the building.
A source has said staff were shocked and upset by the news. "John is a great guy to work with, he will be missed."
There was no answer at Campbell's Grey Lynn home when an NZME. News Service reporter visited shortly after the announcement this afternoon.
Jennings said the review of the show assessed a series of options, and an "evolution of current affairs at 7pm emerged as the best option for improving commercial performance of the prime time 7pm slot on TV3".
"As much as anything, this was a review of the viability of current affairs at 7pm," Jennings said. "We went in without any preconceived idea of the outcome, but with a clear goal to turnaround the ratings decline.
"The review has clearly shown us what's most relevant to our audience at 7pm is current affairs, but not Campbell Live as we know it.
"We will be bringing the best of Campbell Live over to the new show, but will be looking at a wider mix of stories."
Campbell's next move is unclear, but broadcasting sources have told the NZ Herald that Radio New Zealand has expressed an interest in him joining the team.
RNZ head of content Carol Hirschfeld is a close friend of Campbell, a former TV3 newsreader with him and a former executive producer of Campbell Live.
Hirschfeld started the RNZ job after a difficult legal process at Maori Television where she was restructured out of her job by new chief executive Paora Maxwell.
A source said there had been two approaches, but that just last week it was decided to not proceed further, because it was expected he would be staying on at TV3.
Prime Minister John Key said he wished Campbell well in his next role, and rejected any suggestion that the two men did not get along.
"Despite what some people might think I don't have an adversarial relationship with John," Mr Key said.
"I've gone on his show whenever it has practically suited me to go the show, and sometimes when it hasn't.
"I've found him professional to deal with. He did a good job of chairing the [election] debate ... last time. Off camera we've always had a pretty healthy and respectful relationship.
"I'm not involved in what happens at MediaWorks but obviously I wish him the best for whatever he decides to do from here on in."
Media commentator Bill Ralston, former TVNZ head of current affairs, said the decision was "eminently foreseeable".
"The review had its mind made up from the start," he told the Herald.
"The collective bile of Campbell fans will be rising rapidly. The real challenge for TV3 is developing a new programme that appeals to viewers ... we'll have to see what they replace it with and what it looks like in content."
Watch: John Campbell met with Save Campbell Live supporters:
Ralston had no idea who might be best to take the presenter's seat or seats.
When told the show would be reduced to four days, Ralston said: "And then three, and then two and then one - that's the way these things go."
And as for Campbell's future - Ralston said he would make a "fantastic" radio host or presenter on another show.
"What they had was an apples and orange situation there. Campbell was apples and the show was oranges ... I wish John well for the future."
3News said a new entertainment show would screen at 7pm on Fridays and MediaWorks expects the revamped current affairs show to launch in 6-8 weeks.
According their website, Weldon said MediaWorks' senior management team was unanimous in its decision and believed the new show was the most relevant option for audiences and advertisers.
"Mark Jennings recommended we review Campbell Live because, despite the quality of the show, Campbell Live had lost viewers every year for 10 years, to the point where the show was unsustainable.
"Mark has conducted an extremely rigorous review, and the analysis clearly shows current affairs is our best option at 7pm.
"MediaWorks is 100 per cent behind the new current affairs show, and we are determined to make the programme a success."
Weldon told 3News he wanted to pay tribute to Campbell.
"He has made a huge contribution to TV3 and MediaWorks over the years, and I was hoping this would continue - which is why last November I offered John a three-year contract, which he did not sign. I respect John's decision not to continue at MediaWorks and wish him well."