Professor Farmer undertook his DM thesis in the University Department of Diabetes and Endocrinology at Oxford, having completed vocational training at Thame Health Centre where he worked as a principal in the practice from 1985 to 2000. Between 2001 and 2006 he was a Senior Research Fellow in the Department of Primary Health Care holding an NHS R&D Senior Clinical Scientist Award. He also works as a salaried general practitioner at South Oxford Health Centre and is a Senior Research Fellow in the Diabetes Trials Unit.
He now holds an NIHR Senior Investigator Award. His work focuses on research to improve the self-management of diabetes in general practice including the best use of blood glucose monitoring, supporting adherence to medication, and evaluating the use of telehealth to improve long-term outcomes. He was a Harkness Fellow of the Commonwealth Fund of New York in 1991, one of the first general practitioners to hold this award. He currently has additional roles as Co-Director of the NIHR Thames Valley Comprehensive Local Research Network, Chair of a NIHR Programme Grants for Applied Research Progamme sub-panel, and was Deputy Chair of the NIHR Health Technology Assessment Programme Commissioning Board from 2007 to 2011.