National Party leader Chris Luxon was among those who thanked Ms Ardern “for her service to New Zealand”.
“She has given her all to this incredibly demanding job,” the opposition leader wrote on Twitter.
Australian Prime Minister Anthony Albanese described Ms Ardern as a leader of intellect, strength and empathy.
“Jacinda has been a fierce advocate for New Zealand, an inspiration to so many and a great friend to me,” he wrote.
Canada’s leader Justin Trudeau said she had made an “immeasurable” difference to the world.
But while Ms Ardern was often seen as a political star globally, opinion polls suggest she was increasingly unpopular at home.
She led the Labour Party to a landslide election victory in 2020, capitalising on her government’s strong early response to the pandemic.
But the latest opinion polls put her personal popularity at its lowest since she was elected, and approval of her party’s performance similarly low.
In 2022, Ms Ardern told the BBC her declining popularity was the price her government had paid for keeping people safe from Covid-19.
However, she has also been confronted with a cost-of-living crisis, national fears about crime, and a backlog of election promises put off during the pandemic.
Reaction to her announcement has been varied. One local from her own Auckland electorate told the NZ Herald Ms Ardern was “running away before getting thrown out”, blaming her for increased crime and rising living costs.
For others, like Auckland Pride’s Max Tweedie, she is “one of the greatest prime ministers in New Zealand’s history”.
Those are sentiments shared by New Zealand actor Sam Neill, who said Ms Ardern had faced “disgraceful” treatment from “bullies” and “misogynists”.
“She deserved so much better,” the Jurassic Park star wrote on Twitter.
But Ms Ardern stressed that she was not resigning because she and the party were unpopular.
“I am not leaving because I believe we can’t win the election but because I believe we can and will, and we need a fresh set of shoulders for that challenge.”
Contenders for the job are yet to emerge, but several MPs – including deputy leader Grant Robertson – have ruled themselves out of the contest.
Ms Ardern listed her government’s achievements on climate change, social housing and reducing child poverty as ones she was particularly proud of.
But she said she hoped her legacy in New Zealand would be “as someone who always tried to be kind”.
“I hope I leave New Zealanders with a belief that you can be kind, but strong, empathetic but decisive, optimistic but focused. And that you can be your own kind of leader – one who knows when it’s time to go,” she said.
