The 2020 election will be held on Saturday 19 September, she said at a post-Cabinet press conference.
Labour is seeking a further term to "keep getting the job done", she said.
“I will be asking New Zealanders to continue to support my leadership and the current direction of the Government.
“We are running an established and effective MMP Government, and overseeing a strong economy with low unemployment and growth rates the envy of other countries like Australia and the UK, while making critical investments in health, education and reducing child poverty.
“I’ve always believed that announcing elections dates early is fair. It improves the opportunities for New Zealanders to take part in the democratic process and gives a greater degree of certainty to the political landscape."
Last week, Ardern re-committed Labour to a "relentlessly positive, factual, and robust campaign" and said the party would voluntarily sign up to Facebook's new transparency tool, aimed at stopping anonymous "fake news" style advertising.
Advance voting will start on Monday 7 September 2020.
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