The young Labour party leader - she turned 37 last month - and Auckland MP has been tipped in the past as a future leader.
After a stint as deputy, she was today unanimously elected leader - with Te Tai Tokerau MP Kelvin Davis as her deputy - following a tumultous few days ending with Andrew Little stepping down.
So, who is she?
A sometime DJ, who was once a Mormon, and self-described 'nerd' unafraid to poke fun at herself for the cameras, who holds the Mt Albert parliamentary seat that was Helen Clark's for three terms.
She's made no bones about the importance of family over politics and has peviously said she felt socially conscious from an early age.
Ms Ardern was born in Hamilton and spent time growing up Murupara, a small town in rural Bay of Plenty with a reputation as a base for the Tribesmen gang - a reputation the small community has been trying to shake off in recent years.
''They didn't have the same chances, shoes, lunch at school. I noticed that,'' she told RNZ earlier this year.
Her father Ross was a police officer in the town and went on to serve as Niue's chief of police and the New Zealand High Commissioner to the small Pacific nation after a 40-year policing career.
The family moved to Morrinsville, where Ms Ardern went to school, joining the Labour Party when she was a teenager. In 1999 she packed her bags for university, studying for a Bachelor of Arts in communications.
Growing up in small-town New Zealand was formative.
''That will forever influence the way that I view the job I do and the policies that I have a hand in developing," she said.
''It wasn't until much later that I realised that politics was a way to change the things I saw around me.''
Since rising in popularity, sections of the media have occasionally focused on her looks, a tendency she finds frustrating, anger-inducing, and disappointing.
She grafted, working for Phil Goff and Helen Clark in Wellington, travelling overseas for a stint in London, where she worked as a policy adviser in the UK Cabinet Office, and served as president of the International Union of Socialist Youth.
In her first election, in 2008, she was unsuccessful as the candidate in Waikato, but got voted in via the party list, making her the youngest sitting MP.
She won a landslide victory in the Mt Albert by-election at the start of the year, with 77 percent of the vote, and when Annette King resigned as deputy in March, Ms Ardern was unanimously elected to the role.