Ma Jun is a well-known Chinese environmentalist, scholar, and writer. Starting in 1993, Ma Jun became known as an investigative journalist, reporting on environmental issues for the South China Morning Post. His research interest in China's environment and natural resources led him to write China's Water Crisis (1999), which describes the problems threatening the communities, economies, and environment in China's seven major river basins. In 2000, Ma Jun became the Chief Representative of SCMP.com at the South China Morning Post office in Beijing. In 2002, he began consulting for the Sinosphere Corporation, advising overseas companies with operations in China on environmental, health, and safety regulations and laws in China, as well as helping these multinational corporations to set up social responsibility standards and evaluation systems for their suppliers.

In 2004, Ma Jun was selected for the Yale World Fellows Program, where he completed comparative research on Chinese and American environmental management policies and systems. After returning to China in 2005, he began writing articles exploring the direction that China could take in forming its environmental management and resource management policies. In 2006, Ma Jun was named by Time magazine as one of "The 100 Most Influential People in the World." Also in 2006, Ma Jun founded the Institute of Public & Environmental Affairs (IPE), a Beijing-based, registered nonprofit organization that promotes the disclosure of environmental information and the greening of corporate supply chains in China. Since its founding, the IPE has developed the "China Pollution Map Database," the first public database of corporate environmental performance in China. More recently, the IPE has released comparative reports about the transparency of pollution information (PITI) and air quality information (AQTI) in China and around the world, as well as a series of reports on heavy metal pollution. Ma Jun received a national award in 2006 for his work in the public interest, and an Eco-Award from The Nature Conservancy and the Society of Entrepreneurs & Ecology in 2009. He has written for the online journal China Dialogue since 2006, and is a frequent lecturer and commentator in both domestic and foreign media on matters relating to the environment in China.