UPDATE

Veterans Affairs Minister Michael McCormack has been elected leader of the National Party, and so will become Australia’s new Deputy Prime Minister.

Members and senators elected Mr McCormack, 53, leader at a special party room meeting at 8am in Parliament House where Barnaby Joyce will formally stand down after weeks of fallout surrounding his marriage break-up and a relationship with a former staffer who is now pregnant.

The vote was expected to be uncontested, but in a late development, outspoken MP George Christensen decided to challenge Mr McCormack for the leadership.

Mr McCormack applauded Mr Christensen’s decision to put his hand up, but declined to say how his challenger polled in the vote.

Mr McCormack paid tribute to Mr Joyce and Nationals leaders past.

“I am absolutely indebted to Barnaby Joyce and also his predecessors. Warren truss, my initial leader when I came to Parliament in 2010,” he said. “And before him, Mark [Vaile], John [Anderson], Tim [Fischer] and others, all the way back to our first federal parliamentary leader who, like me, was a newspaper editor.”

EARLIER

Earlier, potential challengers, NSW MP David Gillespie and agriculture minister and Joyce supporter David Littleproud, both withdrew.

Mr Gillespie quit the race on Sunday, hours after acting Nationals leader Bridget McKenzie urged the party to put forward only one candidate.

“Conventionally around leadership, there usually isn’t a vote,” Senator McKenzie told the ABC’s Insiders program.

Agriculture Minister David Littleproud pulled his name from the ballot late Sunday night, saying: “Now is not the time for internal contests.”

Mr Littleproud echoed the call for unity in a statement published by The Australian on Monday morning.

“Now is the time for all individuals to be team players. Now is the time to think about stability and the good of the party,” he said.

Mr Littleproud’s potential candidacy came as some Queensland MPs looked to secure better political representation for their state, The Australian reported.

Despite the desire to avoid a messy leadership contest, it is Mr Joyce’s move to the backbench that the government’s opponents have seized upon.

Mr Joyce, once a rebellious Queensland senator, is set to join the increasingly vocal former prime minister Tony Abbott on the backbench – a prospect the opposition is already trying to exploit.

Seven News reported on Saturday that Mr Joyce was considering challenging for the leadership after the next election.

“Whoever they elect tomorrow, that person can expect to be undermined by Barnaby Joyce,” Labor frontbencher Jason Clare told the ABC.

“He goes back to the backbench, but just like Tony Abbott you can expect him to fester and agitate and try and derail the government from there.

“They’ll be like Statler and Waldorf from The Muppet Show.”

Canberra’s Statler and Waldorf? Labor compared Mr Joyce and Mr Abbott to two cantankerous hecklers from The Muppets. Photos: AAP/Getty

Before he moved to the lower house at the 2013 election, Mr Joyce was a regular thorn in the side of the Coalition leadership.

In October 2005, only three months after taking his place in the Senate, Mr Joyce rebelled on two votes on trade practices legislation, siding with Labor and the minor parties, and infuriating then-Nationals leader Mark Vaile.

In December that year, Mr Joyce crossed the floor again to oppose Prime Minister John Howard’s push to ban compulsory student union membership.

In May 2006, Mr Joyce sought to kill off the Howard government’s efforts to allow oil companies to own more petrol stations, a move the Nationals senator said would kill off ‘mum and dad’ businesses.

Parliamentary Library figures show Mr Joyce crossed the floor 28 times while in the Senate – far more than any other MP or senator over the past 10 years.

He also threatened to rebel on the sale of Telstra, eventually extracting concessions from the Howard government in exchange for his crucial vote.

Despite this, Nationals MP Darren Chester said on Sunday he was confident Mr Joyce would be a “team player”.

“I’ve known Barnaby for 10 years. I’ve known him to be a team player who wants to see regional Australia get ahead,” Mr Chester told Channel Nine.

“I’m sure he’ll be a positive influence on the National Party from the backbench.”

Asked on Friday how he would conduct himself on the backbench, Mr Joyce said he “won’t snipe”.

He will join his Nationals colleague George Christensen, the Coalition’s most prominent rebel, on the lower house backbenches.

Mr Christensen has crossed the floor once on penalty rates and threatened to do so to establish a banking royal commission before the government eventually relented.

On Saturday, the Dawson MP called for the Nationals to end its coalition with “a Liberal Party lurching further away from the values we still hold”.