The two South African women are behind a landmark legal victory to stop South Africa's massive nuclear deal with Russia.
Awarded annually to environmental heroes, the prize recognises community activists for significant achievements.
Makoma Lekalakala and Liz McDaid helped lead the charge against the plan for the country to procure 9,6 gigawatts of nuclear energy from Russia at an estimated ZAR 1 trillion.
After a lengthy legal battle, the Western Cape High Court ruled in April 2017 that government's decision to call for proposals for the procurement of nuclear energy was unlawful and unconstitutional.
Lekalakala, aged 53, is the director for Earthlife Africa. McDaid, aged 55, is the climate change coordinator for Southern African Faith Communities’ Environment Institute.
In a statement, award organisers say their achievement is immense for South Africa.
"Today, any attempt to revive a nuclear deal in South Africa would certainly face strong public opposition and legal precedent thanks to Lekalakala and McDaid’s work."
The Heinrich Boell Foundation is glad to have been able to support their campaign.