The Earthshot Prize is dedicated to efforts to restore and protect the planet by 2030.
Prince William said Ardern, who tomorrow officially leaves Parliament following her shock resignation earlier this year, was one of the people he spoke to when setting up the charity.
“It is an honour to welcome Jacinda to The Earthshot Prize team,” he said.
“Her life-long commitment to supporting sustainable and environmental solutions, along with her experience as Prime Minister of New Zealand, will bring a rich infusion of new thinking to our mission.
“Four years ago, before The Earthshot Prize even had a name, Jacinda was one of the first people I spoke to, and her encouragement and advice was crucial to the prize’s early success.
“I am hugely grateful to her for joining us as she takes the next steps in her career.”
The Earthshot Prize is awarded to five winners each year for their commitment to environmentalism.
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