MB ChB Bristol 1952, ChM 1967.
Sellwood gained his medical education at Bristol University and held house appointments at Bristol Royal Infirmary before serving the RAMC in Hong Kong. In the late 1950s he held appointments at the Royal United Hospital, Bath, Bristol Royal Infirmary, and Sharoe Green Hospital, Preston. He was then surgical registrar at the Hammersmith Hospital and spent a year as a researcher in pathology at the Chester Beatty Institute for Cancer Research. Sellwood returned to the Hammersmith as senior surgical registrar and was also tutor in surgery at the Royal Postgraduate Medical School. He later became assistant director of St Mary's Hospital Medical School and honorary consultant surgeon to St Mary's Hospital, London. In 1970, a new chair was established at the University of Manchester for the development of teaching at the University Hospital of South Manchester (Withington). Sellwood was appointed to this post. His main research interest was the dissemination of cancer cells in the circulation, and was recognised as an expert on breast cancer. He was awarded the Moynihan Fellowship in 1970 and under his leadership, the Withington Hospital was recognised as a centre for breast cancer services. Sellwood retired as professor in 1988 and was made emeritus professor.