In the first significant agreement reached the COP26 climate summit, more than 100 global leaders pledged to stop and reverse deforestation by 2030.
Brazil, where large swaths of the Amazon rainforest have been destroyed, was among the signatories on Tuesday.
The promise comprises about £14 billion ($19.2 billion) in public and private cash.
Experts applauded the initiative but warned that a previous agreement in 2014 had "failed to curb deforestation at all" and that obligations needed to be kept.
Tree felling contributes to climate change by depleting forests, which absorb large amounts of the warming gas CO2.
"We have to stop the devastating loss of our forests," he said - and "end the role of humanity as nature's conqueror, and instead become nature's custodian".
The two-week summit in Glasgow is seen as crucial if climate change is to be brought under control.
The "landmark" commitment was made by "more leaders than ever before," according to UK Prime Minister Boris Johnson, who is hosting the global summit in Glasgow.
The nations that have signed the promise, which include Canada, Brazil, Russia, China, Indonesia, the Democratic Republic of the Congo, the United States, and the United Kingdom (the entire list is available here), cover around 85 percent of the world's forests.
Some of the funds will be distributed to underdeveloped nations to help restore damaged land, fight wildfires, and support indigenous populations.
Governments from 28 nations have also pledged to eliminate deforestation from global commerce in food and agricultural goods such as palm oil, soya, and cocoa.
These businesses contribute to forest loss by removing trees to provide room for animals to graze or crops to thrive.
More than 30 of the world's largest financial institutions, including Aviva, Schroders, and Axa, have also pledged to stop investing in deforestation-related businesses.
In addition, a £1.1 billion fund will be formed to conserve the Congo Basin's second-biggest tropical rainforest.
Prof Simon Lewis, a climate and forests expert at University College London, said, "It is wonderful news to have a political commitment from so many nations to halt deforestation, as well as considerable finance to carry forward on that path."
However, he told the BBC that the world "had been here before" with a proclamation in New York in 2014 "that failed to halt deforestation at all."
