WELLINGTON, New Zealand — No one had expected New Zealand’s Sept. 23 election to be much of a contest. The conservatives were expected to win, again.

But that was before Jacinda Ardern and a wave of support that’s now called “Jacindamania.”

The selection of Ms. Ardern as the Labour Party’s leader on Aug. 1 elevated a 37-year-old woman without the traditional setup of a husband or children to the head of a national party, and this country’s politics have not been the same since.

She is Labour’s youngest leader ever, as at home on social media as she is in policy debates. And she has already attracted global attention for condemning a television commentator’s question about whether employers have a right to know whether a woman plans to become a parent.

“That is unacceptable in 2017,” she told him. “It is the woman’s decision about when they choose to have children.”