A mountaineer and conservationist who had been visiting Patagonia since the early 1960s, Tompkins sought to protect the 17,000-hectare (42,000-acre) tract, most of which was primeval Valdivian temperate rainforest, from future exploitation.

After moving to Reñihué to live full-time with his wife, Kris Tompkins, Doug began developing plans for a larger park, gradually acquiring additional adjacent properties from willing sellers.

While nature-related philanthropy has a long tradition in the United States, large-scale private land acquisition for parks was unfamiliar in Chile, and initially generated skepticism and political opposition.

The land holdings which eventually turned into Pumalín Park, stretched from the border of Argentina to the Pacific Ocean, effectively cutting the country in half.

Over the years of the project's development, confidence has been built, both locally and nationally, as Pumalín Park's public access infrastructure began serving thousands of visitors annually.

Small organic farms with activities such as animal husbandry, cheesemaking, ecotourism, wool handicrafts, and honey production function simultaneously as park ranger stations and visitor information centers.

Among the renovations and new beautiful construction were four farms, a tourism building, two churches, the Puma Verde Market, a community center, two supermarkets, and over two dozen houses, all designed to suit the historic architecture of the area.