Kristine McDivitt Tompkins, the widow of US billionaire Doug Tompkins, is donating 408,000 hectares of land to Chile for national parks to be created, the BBC reports.
Doug Tompkins, one of the founders of the outdoor clothing brand The North Face, died in a kayaking accident in Chile in 2015.
A keen conservationist, he bought up huge swathes of land in southern Chile and Argentina to preserve it.
His widow said Mr Tompkins’ vision had inspired her to make the pledge.
“I know that if Doug were here today, he would speak of national parks being one of the greatest expressions of democracy that a country can realise, preserving the masterpieces of a nation for all of its citizenry,” she said.
The donated 408,000 hectares (one million acres) will form part of a network of 17 national parks in Patagonia covering an area the size of Switzerland.
Chilean President Michelle Bachelet said that it was a “key step to treasuring this giant source of biodiversity and safe keep it in the public interest”.