Haydn is also an environmental writer, being the author of many articles, and four books on the environment - 'Ecosolutions: environmental solutions for the world and Australia' (1991), 'A sense of Wonder' (2002), 'The Wilderness Knot' (2009) and 'Climate Change Denial: Heads in the Sand' (coming out 2011). He is a member of the Greater Blue Mountains World Heritage Advisory Committee.
At age 18, Haydn started work as an environmental campaigner, seeking to save the largest wilderness in the state of NSW (now Wollemi National Park). He later worked on the NSW rainforest campaign, the campaign to save the Franklin River in Tasmania, the campaign to protect the Daintree/ Wet Tropics rainforest in Queensland, and the campaign to create the Gardens of Stone National Park in NSW, which now protects some of the unique 'pagoda' rock formations. He is currently on the Executive Boards of the Nature Conservation Council of NSW and the Colong Foundation for Wilderness.