More than 100 world leaders will promise to end and reverse deforestation by 2030, in the COP26 climate summit’s first major deal.
Brazil – where stretches of the Amazon rainforest have been cut down – will be among the signatories on Tuesday.
The pledge includes almost £14bn ($19.2bn) of public and private funds.
Experts welcomed the move, but warned a previous deal in 2014 had “failed to slow deforestation at all” and commitments needed to be delivered on.
Felling trees contributes to climate change because it depletes forests that absorb vast amounts of the warming gas CO2.
UK Prime Minister Boris Johnson, who is hosting the global meeting in Glasgow, will call Tuesday’s deal a “landmark agreement to protect and restore the Earth’s forests”.
“These great teeming ecosystems – these cathedrals of nature – are the lungs of our planet,” he will say at a COP26 event later where world leaders are meeting to discuss forests and land use.
The two-week summit in Glasgow is seen as crucial if climate change is to be brought under control.
