Duncan is a salaried GP at Montpelier Surgery, Brighton and Senior Lecturer in General Practice at the Brighton and Sussex Medical School, where he runs clinical and community practice in phase 1, is the deputy lead for curriculum development, and the lead for medical education research. His own research in medical education has included a focus on supporting learners and practitioners with disabilities, learning difficulties and mental ill-health. In general practice, he leads for the PCN for trans healthcare and has further interests in medical education and mental health. Along with Dr Rupert Payne from Bristol, he is the co-chair of the Society for Academic Primary Care. He is passionate about understanding and addressing health inequalities faced by marginalised communities.