Walter was consultant paediatrician (inherited metabolic disorders) to the Willink Biochemical Genetics Unit at the Royal Manchester Children's Hospital from 1991. He had qualified in medicine from the University of London in 1978, and gained an MSc in 1989 and MD in 1990. Walter held paediatric posts in Oxford and Bristol, was clinical research fellow at the Institute of Child Health in London, and from 1988 to 1991 was lecturer in child health at the University of Bristol. He was a member of the British Paediatric Association. Walter became FRCP London in 1996 and FRCPCH in 1997.