Jami-Lee Ross doesn't have any chance of keeping hold of his Botany seat, a political commentator says.
Mr Ross' resignation as a National MP will trigger a by-election in the Auckland electorate.
Mr Ross won the seat in 2011 - in a by-election sparked by Pansy Wong's depature from Parliament.
Since then, he has grown his majority in the safe National seat.
At last year's election, he got 61 percent of the vote and had a majority of almost 13,000 over his nearest rival.
But political commentator and former National Party staffer Ben Thomas said Mr Ross does not have any hope of keeping his seat.
He said while Mr Ross had a big majority, National won a similar share of the party vote in the electorate
"It's not as if there is a cult of Jami-Lee in Botany, independent of his status as a National Party MP."
Who National selects as its candidate won't have that much bearing on the outcome of the by-election, Mr Thomas said.
"It's very hard to see how National could lose this with poor candidate selection," he said.
"I think sometimes people over-think by-elections - there's been a lot of talk about the demographic make up of Botany, that it might be better putting a candidate of Asian heritage in. I think that's over-thinking it. I think the most important thing here is its history as a National seat with a National Party vote."
Mr Ross rated his chances of keeping the seat as an independent MP, when he fronted for media yesterday.
"I believe based on what I've done for the Botany electorate for the 15 years in local and central government, that I should continue representing them.
"Do I think that I'll win? I wouldn't be doing this if I thought that there was no hope."
In addition, Mr Ross made another pitch to Botany voters.
"You have an opportunity to elect somebody as an independent who can speak up on your behalf freely, or you can elect somebody who will sit at the National Party backbench, who will sit there nodding and clapping at the appropriate time."
National leader Simon Bridges has vowed to put up a good fight in Botany.
"We'll run a strong campaign in Botany and we'll run to win."
Prime Minister Jacinda Ardern said there were still discussions to be had in the Labour Party about how they would approach the by-election.
"This is a seat that in the past has been a strong National seat, this however is obviously going to be an interesting by-election to say the least, but I need to have a conversation with the Labour Party about what they'd like to do in this race."
Green Party co-leader James Shaw said it was too early to say if his party would stand a candidate.
It will be up to the Prime Minister to announce the date of the Botany by-election, but it is likely to be held before the end of the year.
By-elections come with a price tag of about $1 million for the taxpayer.