Barnaby Joyce quits as Australia's deputy prime minister and Nationals leader

Barnaby Joyce has announced his resignation as Nationals leader and deputy prime minister of Australia after weeks of fallout over his affair with a former staffer and now partner, Vikki Campion, who is pregnant with his child.

Joyce saw his support diminish after the revelation on Thursday night that a sexual harassment complaint had been made against him to the country-based National party, the junior partner in the ruling Liberal-National Coalition.

After earlier dismissing the complaint by a Western Australian woman as “spurious and defamatory”, Joyce told a press conference in Armidale on Friday he could not continue as leader while it was being investigated.

He said he would resign on Monday, clearing the way for an 8am ballot to determine the Nationals leader and deputy prime minister, for which the minister for veterans affairs and defence personnel, Michael McCormack, has put himself forward and is the frontrunner. David Gillespie, the assistant minister for children and families, has also put himself forward.

Joyce said “without a shadow of a doubt” he would remain the member for New England, but did not rule out a return as deputy prime minister. The Nationals whip, Michelle Landry, said he would “focus on clearing his name … [and] will sit at the backbench for the moment”.

Joyce said he had faced a “litany of allegations” that he did not think had been sustained but the sexual harassment complaint was “the straw that broke the camel’s back”.

Thanking the people of his New England constituency and his supporters, Joyce observed: “I don’t deserve the support that you’ve given me.”

He lamented the fact his relationship with Campion had been exposed by the media and the immense pressure she has been under since Sydney’s Daily Telegraph published a photograph of her, visibly pregnant, crossing the road.

“I thought that’s not who we are in Australia. That’s not the kind of people we are. I’m the public figure, go after me.”

Joyce said his resignation should be a “circuit breaker” for the parliament, “for Vikki, for my unborn child, my daughters, and for [my wife] Nat”.

“This has got to stop. It’s not fair on them. It’s just completely and utterly unwarranted, the sort of observation that’s happened.”

In a statement on Friday, Malcolm Turnbull thanked Joyce for his service and boasted that the Coalition had been “Australia’s most successful political partnership”.

“This partnership is undiminished and will continue to deliver opportunity and security for all Australians,” the prime minister said.

Reports suggest Joyce did not call Turnbull before making the announcement, and Joyce himself said he had informed acting prime minister, Mathias Cormann.

Joyce refused to endorse a successor but McCormack is likely to gain support from the party’s social conservative base. Gillespie had also indicated to colleagues that he would put his hand up if Joyce resigned, and he confirmed that on Friday afternoon on 2GB radio.

After dodging the question last week McCormack confirmed he would run for the leadership so the National party could “grow local economies, increase local opportunities and create local jobs”.

“We can do this together as a united team,” he said. “I am a fighter and I have the drive to deliver.”

McCormack, a former regional newspaper editor, entered parliament in 2010, joined the ministry in 2013 and has held various portfolios including small business.

Nationals MPs believe David Littleproud, who was catapulted into cabinet in the December reshuffle after his election in 2016, would also enjoy support. But he has not declared as a candidate.

The former infrastructure minister Darren Chester told ABC Radio that Joyce had made the “right decision” to clear the air in what had become a distraction for the government.

He ruled out running for the leadership, citing the fact he did not have the numbers and the party was “not ready for someone a bit more moderate”.

Chester endorsed McCormack, noting that he was the party’s “most experienced House of Representatives minister”. He told the ABC he would take a ministry position in future if he had the opportunity but was not “applying for a new job”.

It is not considered tenable to have Victorians in both leadership positions. The party’s current deputy, Senator Bridget McKenzie, and Chester are both Victorians.

Landry said senators could not run, which rules out McKenzie and Joyce’s former chief of staff, the resources and northern Australia minister, Matt Canavan.

A generous tribute from Canavan suggested Joyce would “continue [the] fight” for regional Australia. “None of my mates are perfect, nor am I,” he said. “Barnaby has made mistakes but I am sure he will recover, learn and be a better person from them.”

The party’s federal president, Larry Anthony, said Joyce was “a fierce advocate for regional Australia” and would “continue to be a huge asset” for the party as member for New England.

“He made an enormous contribution to the Nationals, highlighted by his herculean efforts to lead the party to our best electoral result in 20 years at the 2016 federal election, which was critical to forming a Coalition government.”

Joyce shot to fame internationally in 2015 when he threatened to have dogs belonging to the actors Jonny Depp and Amber Heard put to death for a breach of biosecurity rules.

In October the high court ruled that Joyce was ineligible to sit in parliament because he was a dual New Zealand citizen, one of nine Australian politicians thus far to resign or be forced out by a rigid but – until recently – little-enforced constitutional disqualification. After a campaign in which he was forced to fend off questions about his private life, Joyce won back his seat of New England in a resounding victory.

At a press conference outside the White House in Washington DC on Thursday, Turnbull repeatedly refused to express support for Joyce.

Before Joyce’s announcement on Friday, a second Nationals MP, Andrew Gee, withdrew his support, backing Andrew Broad’s call for him to stand down and resolve the leadership with a ballot.

The minister for regional development, John McVeigh, will act as infrastructure and transport minister pending the election of a new Nationals leader and ministerial changes.