The search for a successor to Ban Ki-moon comes at a time of high anxiety in global affairs as the United Nations grapples with the biggest refugee crisis since World War II and raging conflicts in the Middle East and Africa.
"I am putting myself forward based on proven leadership experience over close to three decades, both in my own country and here at the United Nations," Clark told AFP in an interview, ending months of speculation.
Currently the UN's highest-ranking woman, Clark heads its largest agency, the UN Development Programme (UNDP), a post she has held for the past seven years, overseeing the world body's vast development agenda.
New Zealand formally put forward Clark, one of the most experienced women in global politics, as its candidate at a press conference in Wellington.
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"Having served as the prime minister of New Zealand for nine years and held one of the top jobs in the United Nations for the past seven, Helen Clark has the right mix of skills and experience for the job," Prime Minister John Key said.
"Coming from New Zealand, Helen Clark is well placed to bridge divisions and get results. She is the best person for the job."
The 66-year-old former academic is among New Zealand's longest-serving prime ministers, having headed the government for three successive terms from 1999 to 2008.
Next week, the UN General Assembly will hold public hearings for the candidates for the first time in the United Nations' 70-year history, with the race still wide open months before a vote.
Clark would become the first woman to lead the United Nations, after eight men in the top job -- although she downplayed her gender as a factor in her candidacy.
"I'm not putting myself forward because I'm a woman. I'm putting myself forward because I think I'm the best person for the job," she said.