Ardern on Tuesday announced the general elections would be held on Sept. 19. She is seeking a second term in office and is expected to face tough competition from conservative challenger Simon Bridges.
Voters will also decide on two contentious social issues in referendums on the same date: whether to legalize euthanasia, and whether to legalize recreational marijuana.
Ardern promised to run "a positive, a factual and a robust" election campaign.
"New Zealanders deserve freedom from misinformation and some of the negative style of campaigning that we have seen take place overseas," she said.
She said her government was responsible for overseeing a strong economy and making crucial investments in health, education and reducing child poverty.
Ardern is seen by many of her supporters globally as the antithesis of President Donald Trump. She was widely lauded for her empathy after a white supremacist gunman attacked two mosques in March, killing 51 Muslim worshippers. She is also seen as a role model of a high-profile working mother after giving birth to a daughter while in office.
But her international acclaim has sometimes been regarded with suspicion at home, where she and her Labour Party remain locked in a tight struggle for support with Bridges' National Party. Polls indicate the election will be a close contest.
"Bring it on," Bridges said in a statement, saying that while Ardern and her Labour Party had promised much, they had delivered little.
"New Zealanders know we will get things done, whether it's more money in your pocket, a stronger economy, less tax, building infrastructure and roads or keeping families safer from increasing gang violence," Bridges said.
Under New Zealand's proportional voting system, which is similar to the model used in Germany, political parties must generally form alliances to govern. That makes the votes won by smaller parties crucial to the outcome. That was the case in the last election, with mercurial politician Winston Peters and his small New Zealand First party choosing to side with Ardern, allowing her to govern.
The scramble for votes appears to be already underway, with Ardern due Wednesday to announce billions of dollars in extra infrastructure spending.
New Zealand holds its elections every three years, with the government deciding the exact date.