Mr Walsh undertook training at the Hammersmith Hospital, National Hospital for Neurology and Neurosurgery, the Institute of Neurological Sciences in Glasgow and completed a specialist fellowship in cerebrovascular surgery training at Royal North Shore Hospital in Sydney, Australia. He also undertook a period of research training at the Imperial School of Medicine and the Thrombosis Research Institute in London.

Mr Walsh is the South Thames Training Programme Director in Neurosurgery and is a member of the National Neurosurgical Selection Panel. He is a reviewer for several international neurosurgical journals and is a member of the editorial panel for two. He serves as an elected representative on Individual Member Committee of the European Association of Neurosurgical Societies (EANS). Through the British Neurovascular Group he has contributed to interdisciplinary training in neurovascular Surgery and National Audit initiatives.