Martyn studied dentistry at Cardiff where he graduated in 1978. He worked as an Associate before moving to Devon in 1984 where he still lives. He bought a NHS family practice and worked there until 2013 when he retired from clinical practice. He has worked extensively in training newly qualified dentists and has been a Vocational Trainer, Vocational Training Adviser and Regional Adviser in General Dental Practice and Associate Postgraduate Dental Dean (DF1) in the South West Region.
He was appointed to the GDC’s Fitness to Practise Panel in 2003, later becoming a chair, and worked in that role until 2013. Currently he is a lay member and a chair of the General Medical Council’s Medical Practitioners Tribunal Service, a dental member of the First-tier Tribunal Primary Health Lists (Health, Education and Social Care Chamber), a lay member of the Probate Committee of the Institute of Chartered Accountants of England and Wales and a Non-executive Director of Dentists' Provident.