Hernandez started working with Greenpeace International in 1995 as coordinator for the environmental group’s toxics campaign in Asia.  It was during this time when he launched the campaign against the ill advised plans of setting up waste incinerators to deal with the burgeoning waste problems of Metro Manila.

Hernandez's campaign exposing the economic pitfalls, environmental and public health hazards of toxics pollution from the burning of waste, quashed these plans. That campaign culminated in the passage of the Philippine Clean Air Act in 1999 which included the first ever national ban on waste incineration. Together with allies in the Philippine environmental movement, Hernandez subsequently and successfully campaigned for the approval of the Ecological Waste Management Act which mandates the segregation of wastes and the development of materials recovery facilities and recycling targets nationwide.

For this work, he was awarded the Goldman Environmental Prize in 2003 , considered to be the equivalent of the Nobel prize for grassroots environmentalists.  Hernandez is the first Filipino to win the prestigious award whose previous awardees include Nobel laureate Wangari Maathai.

As an environmental activist of more than fifteen years, Von has initiated a number of environmental campaigns and projects in the Philippines such as the campaign for the rehabilitation of  the Pasig River, and the crusade to clean-up toxic contaminated sites in the former US military bases in Clark and Subic. He is also a founder  and key driver of various environmental initiatives and coalitions both at the national and international levels including the Global Anti-Incineration Alliance (GAIA), Waste Not Asia,  Lakbay Kalikasan, the Eco-Waste coalition, the Sagip Pasig Movement, and the People’s Task Force for Bases Clean-up.

He is now the Campaign Director of  Greenpeace Southeast Asia where he directly oversees the environmental group’s campaigns on climate change, toxics and water pollution, forests, and sustainable agriculture.