The National Party has elected Judith Collins as its new leader to replace Todd Muller, with Gerry Brownlee as her deputy.

Collins, 61, was first elected as an MP for Clevedon in 2002 and has been part of six Parliaments.

"I think it's really important that we all have a common goal ... to get rid of the current government and put in place a better government," she said after emerging from the caucus meeting.

"There is no chance at all that I am going to allow ... Ardern to get away with any nonsense to do with our economy. I am going to hold her to account."

"Most people would have no idea just how hard my colleagues work."

The MP for Papakura has been the shadow Attorney General since May and holds the National party's spokesperson roles for several areas, including Economic Development, Regional Development and Pike River Re-Entry.

She has previously been the minister for ACC, Corrections, energy and resources, ethnic affairs, ethnic communities, justice, police, revenue and veterans' affairs.

"One of the things that unifies any party is if they see that we're getting the results that we want ... I think you're going to find that we're very focused on winning."

According to her National Party profile, she holds a Bachelor of Laws, Master of Laws with Honours and a Master of Taxation Studies from the University of Auckland and was a lawyer and company director before being elected to parliament.

Brownlee said he was there to support Collins "and the rest of the team and that's what I'll be doing".

"I would say experience, toughness, the ability to make decisions ... that would be myself. Jacinda Ardern is someone we should not ever underestimate."

"We're actually better. If you look at our team, our experience ... it's all better than Jacinda Ardern and her team."

He ruled out ever wanting the leadership.

Collins replaces Todd Muller, who resigned this morning, saying it had become clear he was not the best person for the job.

Brownlee offered his sympathies.

"I just was devastated for Todd Muller and his family, I found Todd a wonderful person to work with ... I'm sure he will continue to be just that."

Much as her predecessor had, Collins confirmed at her first speech Paul Goldsmith would remain the finance spokesperson.

The party would continue to support Muller in what was a difficult time, Collins said. She said it was important that National MPs had no further distractions before the election.

Muller was elected as a new MP for the Bay of Plenty in 2014. He took over the leadership after rolling Simon Bridges in May.

His was a short leadership, lasting only 53 days.

Collins' history with scandal or controversy:

• Dirty Politics 2014: She was accused of leaking information to her friend and right-wing blogger Cameron Slater in the book Dirty Politics. She resigned from Cabinet after allegations she tried to undermine the Serious Fraud Office director. An inquiry cleared her of wrongdoing. She was reinstated in 2015.
• Oravida 2014: She visited the Shanghai offices of Oravida, of which her husband is a director, while on a taxpayer-funded trip. The company used her photo as a product endorsement.
• Wetlands comments 2014: It emerged swamp kauri had been stockpiled in Northland under the name Oravida Kauri, another business linked to Oravida and Ms Collins' husband. She outraged environmentalists by telling a reporter she did not care, saying, "Am I the Minister of Wetlands?"
• Brownlee was among former National ministers forced to defend the activities of private investigators under their watch after it emerged insurer Southern Response broke its code of conduct when it used security firm Thompson and Clark to secretly record meetings of earthquake victims. As former Earthquake Recovery Minister Brownlee took issue with the report, saying it used "inflammatory language that's designed to make the big cost of it more palatable."

Republished by arrangement