A fourth candidate has joined the race for the National Party leadership - former police officer Mark Mitchell.
Mr Mitchell said he was approached three weeks ago by caucus colleagues urging him to run if the leadership came up.
National's Bill English announced his resignation last Tuesday, saying he had only informed his caucus colleagues of his decision to resign that morning.
While Mr Mitchell may be lacking public profile and extensive Government experience, he is seen as a likeable candidate.
"I am entering the race because I want to win," he said as he announced his candidacy on Monday afternoon.
Mr Mitchell said he is discounting the role of deputy.
"I am able to build a team. One thing I'm very serious about is actually holding this shambolic Government to account," he said.
Mr Mitchell worked for the police, before leaving to run an international security and hostage rescue business. He helped establish emergency response teams in countries hit with natural disasters.
He entered Parliament in 2014. Since then, he's had a short stint as a Minister, picking up Land Information and Statistics portfolios in December 2016. He was shuffled from Statistics to Defence Minister in May 2017 - something of a promotion - he joined the Cabinet team.
Mr Mitchell launched his bid in his north Auckland electorate of Rodney on Monday afternoon.
The 57-member National Party caucus (that is, the MPs elected to office) will decide on the new leadership next Tuesday.
Mr Mitchell said he can earn the support of his caucus colleagues and lead the party to a "stunning" win in 2020.