Just one day into her new job with the centre-left Labour Party, the 37-year-old had already been asked twice in two separate interviews about whether she intended to become a parent.
Ms Ardern responded with good grace to the initial line of questioning, giving a non-committal answer saying it was a dilemma lots of career women faced.
“I'm not pre-determining any of that, just like most of the women out here who just make their lives work,” she told TV3.
But she took exception when told on the same network that New Zealanders had a right to know her plans for parenthood before they decided whether or not to vote for her as prime minister.
Ms Ardern said women should be employed on their qualifications, regardless of their baby-making plans.
“It is totally unacceptable in 2017 to say that women should have to answer that question in the workplace,” she said.
“It is the woman's decision about when they choose to have children. It should not pre-determine whether or not they get the job.”
The grilling by cricketer-turned-TV host Mark Richardson lit up social media, with many commentators saying a man would not face similar questioning.
"Quite frankly, whether a woman intends on having children or not is none of their bloody business," New Zealand human rights commissioner Jackie Blue said.
"Oh, and by the way, it's illegal to ask those questions as they breach the Human Rights Act."
Rights group Women Aoterearoa NZ tweeted: “Yes much work to do – sexism needs to be expunged."
Madeleine Holden, a commentator on pop culture website thespinoff.co.nz, said it was a “retrograde debate” that shifted the focus from Ms Ardern's policies.
“Asking Ardern about her plans to have children implicitly reinforces the sexist notion that a woman’s primary role is motherhood, no matter how accomplished she is in other areas,” she wrote.
Ms Ardern assumed the leadership from Andrew Little on Tuesday after polling showed Labour was heading for a disaster at the September 23 general election.
She will attempt to prevent Prime Minister Bill English winning a fourth term for the centre-right National party-led coalition.
