Speaking to reporters in Whakatane, Ardern said "now is the time to provide New Zealanders with certainty".
She said the policy shows people that a Labour Government would keep a lid on debt, and not make cuts to health and education.
"This is the totality of our tax policy," the Labour leader said, when asked if more was coming.
She pointed out that this puts New Zealand on a lower tax rate than Australia.
"This is a tax rate that is best for New Zealand for our times."
For her, the new tax was about maintaining core services while only impacting a few New Zealanders.
Ardern said claims made by National that today's announcement was "just the beginning" and that "Labour will eventually widen the net and come after middle-income earners" was just "misinformation".
She said the party has outlined the totality of its tax policy today.
Ardern added that National's statement was just "opposition politics".
How much more will Kiwis pay
Labour's promised tax would impact those earning $200,000 a year roughly $23 a week – $1200 a year – but would generate up to $550 million a year.
Robertson said the tax was about maintaining investment in important services for New Zealanders, while keeping the tax rate exactly the same for the vast majority of the country.
"Our plan strikes a balance as we recover from Covid-19," he said.
"It will avoid the cuts to services being suggested by the National Party, and also help keep a lid on debt as we support the economic recovery from a 1-in-100 year shock."
It is about the top earners in New Zealand pitching in "a little more" to help pay for the country's essential services, in the wake of Covid-19.
For 98 per cent of the country, Robertson said there would be no changes to income tax.
"Labour will not implement any new taxes or make any further increases to income tax next term," Robertson promised this morning.
This is in addition to Labour's promise not to raise fuel taxes if it wins re-election in October.
"Our team of five million is doing an outstanding job in the fight against Covid-19. It's important that peoples' incomes and services are protected as we recover and rebuild."
Labour's revenue spokesman Stuart Nash said that in Australia, people earning above A$180,000 a year pay a 47 per cent tax rate.
In fact, the new top tax bracket still means that New Zealand is in the bottom third of the 36 OECD countries when it comes to a top tax rate.
The company tax rate is not changing, Nash confirmed.
He said that this would give businesses "continuity and certainty".
Robertson said the new tax revenue would also help pay down New Zealand's debt – debt taken on to help jump-start the economy as it battles with the Covid-19 economic fallout.
"I have made it my focus over this term of government to manage our books carefully and bring down debt. That focus will continue."
Meanwhile, Nash said a Labour Government is prepared to implement a Digital Services Tax (DST).
Current projections from IRD estimate a DST will raise between $30 million and $80 million of revenue a year, he said.
What the tax thresholds would look like under a re-elected Labour Government:
• Any income up to $14,000: 10.5%
• Extra income over $14,000 and up to $48,000: 17.5%
• Extra income over $48,000 and up to $70,000: 30%
• Extra income over $70,000 and up to $180,000: 33%
• Extra income over $180,000: 39%
