Newsom-Davis came late to medicine; he was delayed because he was piloting jet fighters in the Royal Air Force in 1951 to 1953. In 1954 he entered Cambridge University, where he played varsity hockey; he received a BA degree in 1957. He then enrolled in the Middlesex Hospital Medical School, where he gained his MD in 1966. He was a house physician at the National Hospital for Neurology and Neurosurgery (Queen Square) from 1966 to 1968. After coming to New York for research training with Fred Plum, Newsom-Davis' first papers were about pulmonary function in health and disease. For the next decade, he was a consultant neurologist at Queen Square and the Royal Free Hospital. In 1980, he was made MRC Clinical Research Professor of Neurology, and in 1987, he became professor of clinical neurology at Oxford. There, with Angela Vincent, he established a myasthenia gravis unit, where he worked for the next 11 years. He continued as professor and honorary consultant until his retirement in 1998.