It was dubbed 'Jacindamania' and the 'Jacinda Effect', and it worked. On October 19, 2017, Labour Party leader .
Ms Ardern, 37, reinvigorated Labour's base and armed her party with the best chance of winning the country's general election on September 23.
But she couldn't do it alone. She didn't win enough seats to form government.
Almost four weeks after the poll, populist kingmaker Winston Peters came to the rescue. He backed her over the National Party leader and current Prime Minister Bill English. She then had the numbers to form a coalition government with Mr Peters' New Zealand First and the Greens.
Who is Jacinda Ardern?
Ms Ardern lags behind Mr English in terms of political office experience. She was elected to parliament in 2008 after joining the Labour Party when she was just 17.
The 37-year-old worked for former Labour leader Phil Goff's office and credits former prime minister Helen Clark for inspiring her during her three years in the UK as a public servant in the Cabinet Office, and the Department for Business and Enterprise.
The daughter of a veteran New Zealand police officer, she served as an assistant director for the department where she worked on regulatory issues.
"I spent most of my time... talking to small businesses, local authorities, and even police officers, trying to understand the delicate balancing act between creating a regulatory environment that protects citizens whilst also allowing business and public services to flourish," she told parliament during her maiden speech.
"I am very mindful of the importance and the need for both. With a strong economy comes the chance to further strengthen public services and create a fairer society for everyone."
The New Zealand Labour leader is seen here surrounded by crowds of people in Auckland. Source: Getty Images
Ms Ardern was also president of the International Union of Socialist Youth, an organisation made up of more than 150 progressive youth movements across the globe.
"This role has sent me to some far-flung places around the globe, from Bhutanese refugee camps to the people of Western Sahara, to Lebanon, and to Jerusalem and the West Bank and the wall that divides the two," she said.
In her maiden speech, Ms Ardern referred to herself as a "social democrat" who "believes strongly" in the "values of human rights, social justice, equality, and democracy, and the role of communities".
Among many other issues, she is a big advocate of climate change, wants to reduce poverty and homelessness in the country, give young New Zealanders free tertiary education and decriminalise abortion.
During a leaders' debate, Ms Ardern pledged to take abortion out of the Crimes Act.
"It should be out of the Crimes Act, I’m very clear on that. People need to be able to make their own decision," she said.
"I accept there will be people out there who disagree with abortion I want them to have that as their right. But I also want women who want access to have it as their right too."
Ms Ardern also took aim at Australian students during the debate, according to online news site Stuff, saying: "There's been talk of New Zealanders being locked out of having the same access to tertiary education in Australia as Australian students.
"Our view is that if those rights are removed, we should likewise do the same for our subsidised tertiary education in New Zealand.
"On benefits I hold a different view. We're still fighting for New Zealanders' rights in Australia, I think we should maintain the moral high ground that it's only right that if you pay taxes, you have access to those benefits."
'She's not afraid to get up close and personal'
But it is not just her policies and beliefs that helped her gain popularity.
Massey University’s political expert Grant Duncan, based in New Zealand, says her approachable personality is also appealing to voters.
“She combines a very quick wit and a sharp intelligence with quite a genuine and warm and empathetic way of expressing herself, so people find it very appealing,” he told SBS World News last month.
“Wherever she goes she gets mobbed by people, this is something that happened to [former prime minister] John Key as well, which is a sign of a very popular leader.
“What I’ve noticed about her she is happy to get close to people, she’s not afraid to hug people, she loves taking selfies with pretty much anyone who wants one.”
Ms Ardern's personality most notably came out during a fiery exchange with New Zealand television host Mark Richardson after he suggested it was acceptable for employers to ask women of their baby plans.
"It is totally unacceptable in 2017 to say that women should have to answer that question in the workplace," she said on TV3 in August.
"It is a woman's decision about when they choose to have children. It should not pre-determine whether or not they are given a job."
The Wall Street Journal has compared her to Canada's beloved Prime Minister Justin Trudeau but said her immigration policy was similar to Trump's.
"Ms Ardern's rapid ascent owes much to tapping into growing unease about affordability, particularly among young voters, and feeding off a global backlash over immigration," the article read.
The Labour Party has previously said it was looking at slashing net migration in New Zealand by 20,000 to 30,000 a year.
Not adverse to a selfie
Prof Duncan said her engagement on social media also had contributed to her success.
Ms Ardern has converted her campaign slogan to a hashtag - "Let's Do This".
“She has a very strong presence on Facebook, for example. You can easily look up video of her on the campaign trail,” he said.
“So I guess that ability to use those contemporary techniques that are all important to just relating to the public, she’s very good at it.
“She’s not just good at using those techniques, people want to be associated with her, people approach her and she makes herself very approachable.
“You can see it in many of the videos of her on the campaign trail. People come up to her and she smiles and she’s very warm, she doesn’t mind giving people a hug, so a very personal touch seems to be working for her.”
She has been described as warm and approachable, which makes her more personable to the public. Source: Getty Images
Restoring stability
In the years following Ms Clark’s departure, the Labour party has gone through a period of instability with four changes of leadership.
Phil Goff took up the post after Ms Clark resigned as leader following her election loss to Mr Key, ending her nine-year reign as prime minister.
Mr Goff was succeeded by David Shearer who was then eclipsed by David Cunliffe before Andrew Little became the leader.
Now with the installation of Ms Ardern, Prof Duncan said the party supporters’ base felt energised.
“The Labour Party has been kind of stuck in the middle between two other parties - on the left the Greens party and in the centre the New Zealand First party - and with our system of proportional representation it’s meant that those two parties on either side of Labour have been able to get a reasonable number of seats in parliament," he said.
“That means that people looking at the opposition have looked at what appeared to be a fairly potentially unstable three-party Coalition as an alternative to the present National-led government.
“I think it’s very much to do with that perception of an unstable opposition with uninspiring leadership and often a somewhat undecided really where it stands ideologically. Those sorts of problems have dogged Labour for the last nine years.”
Reaching across generations
Ms Arden’s appeal to younger voters is obvious with her focus on social and environmental policies.
But she has also covered her bases by drumming up support with older generations by comparing current social issues with those of the past.
“For example, she rather cleverly in her campaign launch speech referred to climate change as her generation’s nuclear-free moment,” Prof Duncan said.
“Australians might recall that the shift to a nuclear-free policy was probably the most positive, progressive aspect of the fourth Labour government… back around 1984-85.
“She wants to obviously reach out both to the younger and older generation by bringing this very important this future-orientated issue of climate change to be in a way to compare positively to the nuclear-free policy.”
