Ecocide is defined as “unlawful or wanton acts committed with knowledge that there is a substantial likelihood of severe and either widespread or long-term damage to the environment being caused by those acts”.
The call comes from the first Global Citizens’ Assembly after a vote by members.
The move could see governments, businesses and individuals found guilty of international offences.
In its new declaration, the assembly stated: “Ecocide has to be codified as a crime in the international and national laws, applicable to governments and corporations.
“It has to be firmly enforced alongside existing environmental protection laws.”
The Global Assembly is a newly created piece of infrastructure that ensures everyday people can contribute to global governance.
It comprises a Core Assembly and Community Assemblies and is supported by United Nations secretary general António Guterres and COP26 president Alok Sharma.
The Core Assembly is made up of 100 citizens, chosen to accurately represent the world's population by gender, age, location, education and attitude to climate change.
Members have been selected through a global lottery based on Nasa population data, meaning that anyone alive could be picked.
Any person in any part of the world can take part by running or joining a Community Assembly, with world-class experts on hand to offer information and help in understanding the climate and ecological crisis.
Global Assembly member Chom Chaiyabut, from Thailand, said: “As a leader of my village who fights for mother nature in my community for all my life, I believe the power of citizens’ assemblies such as the Global Assembly will pave the way for the fair and effective action we wish to see towards climate change.”
The Global Assembly, which convened for the first time this year, presented its full declaration for action at an event in the COP26 Green Zone on Monday.
First Minister Nicola Sturgeon attended the launch and members also agreed to endorse the Paris Agreement and its aims to limit global heating to 1.5C.
The assembly resolved that the treaty “has to be strictly enforced and monitored by the United Nations, in collaboration with the relevant actors at all levels of governance”.