In 1937 he went to the USA as a Commonwealth Fund fellow, studying under Paul Dudley White at Harvard Medical School and Massachusetts General Hospital.
[2] In 1938 Spillane was awarded a Harvard research fellowship and studied at the Neurological Institute of New York affiliated with Columbia University College of Physicians and Surgeons.
After the end of WWII he spent a year at the National Hospital for Neurology and Neurosurgery, Queen Square, London.
He was appointed in 1946 an assistant physician to the Cardiff Royal Infirmary and then a consultant neurologist there, as well as an honorary lecturer at the Welsh National School of Medicine.
His clinical research, teaching, and writing helped to establish an international reputation for the Cardiff Royal Infirmary's department of neurology.