The 16-year-old Swedish climate activist said she spent months deciding how to travel to the US without travelling by plane, which she shuns because of their high greenhouse gas emissions.
Ms Thunbeg will set sail on her trans-Atlantic voyage in August in a boat fitted with solar panels and underwater turbines to generate zero-carbon electricity on board. The journey will take two weeks.
“Good news! I’ll be joining the UN Climate Action Summit in New York, COP25 in Santiago and other events along the way,” she tweeted on Monday.
“I’ve been offered a ride on the 60ft racing boat Malizia II. We’ll be sailing across the Atlantic Ocean from the UK to NYC in mid August. #UniteBehindTheScience”.
Ms Thunberg will be accompanied on the voyage by Malizia II’s skipper Boris Hermann, her father Svante and filmmaker Nathan Grossman.
The teenage climate activist told AP that she wanted to avoid travelling to the US by cruise ship because of their notoriously high emissions and she had been wary of sailing across the Atlantic in August due to the risk of hurricanes.
“Taking a boat to North America is basically impossible,” she said. “I have had countless people helping me, trying to contact different boats.”
The founder of the “School Strike 4 Climate" movement said she is taking a year off school to raise awareness of the climate crisis and pressure world leaders to step up efforts to cut greenhouse emissions.
Setting sail from London, Ms Thunberg will attend the UN Climate summits in New York on 23 September and in Sanitago, Chile, on 13 December.
She also plans to join large-scale climate demonstrations in New York on 20 September.
Ms Thunberg rose to prominence last year after she started started skipping classes to protest outside the Swedish parliament.
Her protest inspired millions of other children around the world to walk out school on Fridays to demand greater action on climate change.
Since emerging as the leader the school strike for climate movement, Ms Thunberg has spoken to policymakers at last year’s UN climate conference in Poland she has attended the World Economic Forum in Davos and business leaders at the World Economic Forum in Davos.
In April, the climate activist met party leaders in Westminster and delivered a speech to parliament.
But Ms Thunberg says she was unsure how her message would be received in the US, where Donald Trump has dismissed the need to tackle climate change
Mr Trump announced that the country would withdraw from the Paris climate agreement and his administration has removed a quarter of all references to climate change from federal government websites since 2016.
Ms Thunberg said that meeting the US president would be “just a waste of time”.
"He obviously doesn't listen to the science and the scientists,” she said. “So why should I, a child with no proper education, be able to convince him?"
The teenage climate activist is also to appear on the front cover of Vogue as one of 15 women describes as “trailblazing changemakers” in a special issue of the magazine guest edited by Meghan Markle, the Duchess of Sussex.
Additional reporting by AP