He was trained in anthropology and documentary filmmaking at the Granada School for Visual Anthropology, University of Manchester. He then began working in the Middle East as a photojournalist focused on conflict, culture and the environment. His photographs have been published in newspapers and magazines such as Newsweek, Paris Match, Le Monde, New York Times, Los Angeles Times, Liberation, the Guardian and the Sunday Times. Martyn has produced stories for non-governmental organisations such as the Landmine Survivors Initiative and the International Commission on Missing Persons. He lived in Iraq for two years covering the fight against Islamic State and is now based in Amman, Jordan, continuing to work throughout the Middle East.