The end goal, organisers said this week, is a legal treaty under which states can be brought to justice for flouting the rights of a group or individual.
The initiative comes just weeks after President Donald Trump announced that he would pull the United States out of the 196-nation Paris Agreement on curbing dangerous global warming.
The new pact, being blueprinted by top legal minds from several countries, should eventually be put to the United Nations for adoption, and impose legally-binding obligations on signatory states, its drafters say.
"We already have two international (human rights) pacts... The idea is to create a third, for a third generation of rights -- environmental rights," said French judicial expert Laurent Fabius, who will chair Saturday's meeting.
The earlier covenants -- one for social, economic and cultural rights, the other for civil and political rights -- were adopted by the UN in 1966.
Fabius, who chaired the 2015 UN conference that approved the hard-fought Paris Agreement, said the new text should outline rights and duties, provide for reparations to be made in case of a breach, and introduce the "polluter pays" principle.
It would mean that people can bring states to court, "to have them held responsible or to compel them to adopt laws that are more protective of the environment," explained Yann Aguila of the French Club des Juristes, a think-tank involved in the project.
Participants in Saturday's meeting would include ex-California governor-turned climate campaigner Arnold Schwarzenegger, former UN chief Ban Ki-moon, as well as high court judges from several countries.
The meeting will be closed by President Emmanuel Macron of France, which after Trump's announcement pledged 30 million euros ($34 million) to fund the work of foreign climate researchers on French soil.