John Harrison was appointed Senior Lecturer in Occupational Medicine at the University of Newcastle-Upon-Tyne, in 1990. In 2003, he moved to become Clinical Director of Organisational Wellbeing at the Hammersmith Hospitals NHS Trust / Imperial College Healthcare NHS Trust. He joined the police in 2014 as Chief Medical Officer for Devon and Cornwall Police and became National Police Chief Medical Officer in 2022. He was Academic Dean of the Faculty of Occupational Medicine at the Royal College of Physicians, chair of the European Schools of Occupational Medicine and a board member of the International Commission of Occupational Health (ICOH).