Simon qualified from the London Hospital Medical College in 1986. He was the first principal in general practice to be awarded a Wellcome Trust Health Services Research Fellowship during which he obtained training in clinical epidemiology and public health at the University of Southampton and the London School of Hygiene and Tropical Medicine. He was appointed as University Lecturer at the University of Cambridge in 1998. In 2005 Simon joined the MRC Epidemiology Unit as Assistant Director and was appointed Professor of General Practice in May 2013.
Simon is a Group Leader in the Medical Research Council Epidemiology Unit and CEDAR (the UKCRC Public Health Centre of Excellence for Diet and Activity Research, Honorary Professor of General Medical Practice at Aarhus University Denmark, Honorary Doctor Umeå University Sweden, Honorary Consultant at Cambridge University Hospitals NHS Foundation Trust, NIHR Senior Investigator and Fellow of the Academy of Medical Sciences and the Royal College of General Practitioners.
He undertakes two surgery sessions per week as an unpaid Assistant General Practitioner at a 7-partner, 9850 patient, vocational training practice in the centre of Cambridge.