Barnaby Joyce says sexual harassment allegations against him are false but they were the final straw that led him to resign.
The deputy prime minister will officially quit as Nationals leader on Monday and go to the back bench, but he is not endorsing a successor.
Mr Joyce has spent 16 days fighting off accusations of improper conduct over his affair with his now-pregnant former staffer Vikki Campion, whose moves to two other political offices are under scrutiny.
"Over the last half a month, there has been a litany of allegations. I don't believe any of them have been sustained," Mr Joyce told reporters in Armidale on Friday.
"(But) to give these people in the weatherboard and iron, in those regional and small towns the best opportunity, this current cacophony of issues has to be put aside."
The National party executive is investigating a woman's claims that Mr Joyce sexually harassed her in 2011 - he denies the claims and wants them referred to the police.
But he says reading the allegations on Friday morning prompted him to quit.
"I just thought 'that has to be the straw that breaks the camel's back'," he said.
On Wednesday, Mr Joyce told Fairfax he would ride out the storm, but just two days later he said it was "not hard at all" to decide to step down.
"It's incredibly important that there be a circuit-breaker, not just for the parliament, but more importantly, a circuit-breaker for Vikki, for my unborn child, my daughters and for (wife) Nat," Mr Joyce said.
He also says he won't "snipe" from the back bench.
"I want to assist my colleagues, where I can, to keep their seats and also, quite naturally, in April, a baby will be born. I'll have other things on my mind," he said.
The rugby-loving member for New England said leading the Nationals had been an "incredible honour".
"If you're a Wallaby for 10 minutes, you're a Wallaby for life," he said.
The next Nationals leader will be chosen at a party room meeting on Monday.
Mr Joyce had been Nationals leader since February 2016, apart from a short stint when he had to quit parliament because he was a New Zealand citizen.
