She had been "really keen" for the campaign chair role, having ran the successful Northcote byelection campaign last year.
She would continue to represent Upper Harbour until the election, but moving to the list would free her of campaigning for that seat during the 2020 campaign.
The seat is a safe one for National, with 54 per cent of voters supporting National in 2014 and in 2017, slightly less than the 56 per cent support that Bennett received in the candidate race.
It would be an opportunity for renewal to bring a new MP into a safe seat, and Bennett said there would a lot of local interest, though she would not be endorsing anyone in particular.
"I think there will be a number of people who will put up their hand. This is for our members and for the party to select a candidate."
She would miss being an electorate MP, she said.
"I love it, and I love my electorate, but you can't do everything.
"This campaign is going to be one of the biggest I've been involved, and I reckon it needs everything I've got, and I want to put everything into it.
"It's only fair to my constituents that they have someone who can give 100 per cent as well."
National has traditionally only had a few senior MPs as list-only.
In 2017 they were Sir Bill English, who moved to the list in 2014, Steven Joyce, who was also the 2017 campaign chair, David Carter and Jian Yang.
"It makes sense for the party, it makes sense for my electorate, and it makes sense for my family," Bennett said.
New Zealand First leader Winston Peters said it was "amateur hour" for National to give Bennett the job of campaign chair.
"What qualifications to run a campaign has she got?
"This decision is so that the National Party can axe her prior to coalition negotiations in 2020, after they've realised that Vernon Tava and his planned Sustainability New Zealand Party is a headless chook, albeit being fed organics."
National has not ruled out working with Sustainability New Zealand, which would need 5 per cent support or an electorate seat to have MPs in Parliament.
Tava, who has recently said that he is close to the 500 members needed to register a political party, has been contacted for comment.
National Party president Peter Goodfellow praised Bennett's work in the Northcote byelection, won by Dan Bidois.
"She brings the right level of skills, energy and enthusiasm we need to run the most comprehensive campaign we can deliver," Goodfellow said in a statement.
"National is well underway in our 2020 campaign preparations. Our candidate selection process has already begun, we've appointed our campaign chair, and our wider organisation of tens of thousands of members, volunteers and supporters are gearing up to fight this campaign with everything we've got."
