Ardern said at the time that she no longer had "enough in the tank" to do the job well, leading some people to speculate it was burnout that led her to leave the high-profile job.
In a new interview with "Good Morning America" co-anchor Robin Roberts, Ardern dispelled the myth that she was experiencing burnout as both a woman and a mom in the role.
"I could have kept going but, for me, having been through a period where we did experience a lot of crises in New Zealand, it was whether or not I had enough to do the job well, and the answer for me personally was, no, it was time for someone else," Ardern told Roberts in a live interview Wednesday. "So, a bit different than burnout."
Burnout is defined by the World Health Organization as a condition "resulting from chronic workplace stress that has not been successfully managed." In 2019, WHO called burnout an "occupational phenomenon" and included the condition in its International Classification of Diseases, a diagnostic tool for medical providers.
Ardern said that though it was not burnout that led her to step down, she recognizes the impact she had in speaking out publicly about why she chose not to seek reelection and in being honest that it was time for a new leader for her country.
"I was overwhelmed by the fact that beyond New Zealand's shore, it triggered a discussion about how we make these decisions," Ardern said. "I had particularly a few women say to me, 'Thank you for making it OK to say that I'm tired or that I don't have enough in the tank to do a job well.'"
She continued, "I think we carry a huge sense of responsibility to just keep going."
Part of both the burden and privilege Ardern carried with her as prime minister was that she was different than prime ministers of the past.
She was the youngest prime minister in New Zealand in more than 150 years and only the second elected world leader in modern times to give birth while in office.
Ardern told Roberts that she hopes her time as the country's top leader inspired other people around the world to step up and serve, saying, "I hope it was a call to anyone who is holding themselves back."
"I think it might have been perhaps a call to other reluctant leaders, to those out there who may think that they don't have the character traits or they see themselves as too sensitive, not tough enough or [see] roles in leadership, particularly politics, as being a place where that would be a hard set of character traits to bring to the table," Ardern said, adding, "I think they're necessary ones."
She continued, "If you're sensitive enough, it means you're empathetic. We need more empathy in leadership. We need more kindness in leadership."
Since finishing her final term as prime minister, Ardern said she has worked to fulfill her promise of spending more time with her family.
She gave birth to her daughter in 2018, the first child for her and partner Clarke Gayford.
"One of the things I wanted to do was be more present for my family, so I'm certainly trying to do that," Ardern said. "But also I still want to be useful."
For Ardern, being useful has meant serving as a fellow at Harvard University in Boston, continuing her work to lessen the amount of extremism and terrorism online, working with Britain's Prince William on his Earthshot Prize initiative and writing a book.
"I didn't want to write about the small, individual political things that happened in New Zealand over the past five years," Ardern said. "But then someone expressed to me in a different way, 'What if you just wrote about what it was like as a human?' And so they changed my mind, and now I'm really just writing a few stories."