Dr. Reynolds qualified in Medicine at the Welsh National School of Medicine, Cardiff in 1959. He trained in Neurology at the National Hospital for Neurology and Neurosurgery, Queen Square, London from 1963–1969 and at Yale University Department of Neurology in 1970.

He was Consultant Neurologist to the Maudsley and King’s College Hospitals, London from 1974–1999. He was first Chairman of the Centre for Epilepsy at King’s College Hospital and first Director of the Institute of Epileptology of King’s College, London from 1994–2000; and founding Chairman of the Fund for Epilepsy from 1992–2004.

He served as President of the International League Against Epilepsy (ILAE) from 1993–1997, when he initiated the ILAE/IBE/WHO Global Campaign Against Epilepsy of which he was first Chairman from 1997 – 2001. This Global Campaign continues and since 2022 has become a joint Campaign for Epilepsy and Other Neurological Disorders in collaboration with the World Federation of Neurology (WFN) and other neurological NGO’s.

His research interests have included epilepsy, neuropsychiatry and metabolic diseases of the nervous system, especially folate and vitamin B12 deficiencies. He has co-edited 8 books, published over 250 papers and lectured widely on every continent on these subjects. More recently he has expanded his interest in the history of medicine, neurology, psychiatry and public health, including Babylonian and 19th century neurology and psychiatry.

With his colleagues he: 1) Initiated the first studies of monotherapy and prognosis for newly diagnosed epilepsy; 2) Established the neuropsychiatric manifestations of folate deficiency; 3) Built bridges between neurology and psychiatry; 4) Undertook original research of Babylonian neurology and psychiatry, and also of 19th century neurology and psychiatry, including Robert Bentley Todd, Michael Faraday and the concept of electrical functions and discharges in the nervous system.