7 people were killed around the world in 2020, the highest number recorded for a second consecutive year, the report from Global Witness said.
Almost a third of the murders were reportedly linked to resource exploitation - logging, mining, large-scale agribusiness, hydroelectric dams and other infrastructure.
The report called the victims "environmental defenders" killed for protecting natural resources that need to be preserved, including forests, water supplies and oceans. Since the Paris Agreement on climate change was signed in 2015, the organisation says on average four activists have been killed each week.
It said this "shocking figure" was likely to be an underestimate because of growing restrictions on journalists and other civic freedoms.Logging was the industry linked to the most murders with 23 cases - with attacks in Brazil, Nicaragua, Peru and the Philippines.
Indigenous peoples, most often on the frontline of climate change, accounted for a further one third of cases. Colombia had the highest recorded attacks, with 65 people killed last year.
Those murdered included South African Fikile Ntshangase, 65, who was involved in a legal dispute over the extension of an opencast mine operated by Tendele Coal near Somkhele in KwaZulu-Natal province. She was shot dead in her own living room.
The killings also included Óscar Eyraud Adams, who was murdered in Mexico in September 2020. He was working to help the indigenous Kumiai community in Baja California have better access to water.
A senior campaigner for Global Witness, Chris Madden, called on governments to "get serious about protecting defenders." He said companies must start "putting people and planet before profit' or he warned that "both climate breakdown and the killings" would continue.
"This dataset is another stark reminder that fighting the climate crisis carries an unbearably heavy burden for some, who risk their lives to save the forests, rivers and biospheres that are essential to counteract unsustainable global warming. This must stop''. The organisation called on governments to formally recognise the human right to a safe, healthy and sustainable environment, and ensure commitments made at November's UN climate change conference, COP26, integrate human rights protections.
In response, COP26 president Alok Sharma told the BBC he had "prioritised meeting people on the front line of climate change," to ensure the voices of all are heard."