Mark worked for several international conservation organisations (the World Wide Fund for Nature, in England; the United Nations Environment Programme, in Kenya; and the World Conservation Union, in Switzerland) before going freelance in 1986.

He is now a Senior Consultant to the Whale and Dolphin Conservation Society and Vice-President of the David Shepherd Wildlife Foundation, and he advises other international conservation bodies on a variety of conservation and development issues. In a voluntary capacity, he actively supports a number of charities (see the links page) and spends a lot of time raising funds and awareness for wildlife conservation.