Professor Greenwood was formerly at St Batholomew's Hospital, London before joining the Department of Microbiology at the University of Nottingham Medical School in 1974, where he remained until retirement in 2000. He was Professor of Antimicrobial Science between 1989 and 2000, and is the former Archivist to the British Society for Antimicrobial Chemotherapy. He has contributed more than 200 scientific articles and books on antimicrobial agents over 40 years.