Duncan was born in Derbyshire and moved to Wales when he was a year old. After gaining a degree in Fine Art from the Norwich School of Art, he worked for three years as an art teacher. Inspired by his upbringing in rural Eryri, he then decided to follow a different path and studied Field Biology at the University of London.
Upon returning to Wales, he worked as a nature reserve manager in Gwynedd for almost fifty years and was responsible for various habitats – sand dunes, mountains, marshes and forests. He developed a keen interest in historical ecology and the relationship between nature and people throughout the ages, especially in Wales.
Since retiring in 2009, he enjoys collaborating with Twm Elias and others on the Llên Natur project, which brings together the Welsh language, concern for the environment and an interest in nature. He also loves cycling, gardening and cooking.