Simon qualified in Medicine at Southampton University and trained initially as a general practitioner. He practised as a GP in rural Hampshire for seven years before studying and specialising in public health medicine. He held a number of Consultant and Director of Public Health posts in the south of England. In 2007 he was appointed to the role of Regional Director of Public Health for London and Health Adviser to the Mayor, where he took responsibility for health inequalities strategy and the health service response to the London Olympics. He retired from this post in March 2013.