He started his career as a Psychologist at HM Prison Bristol, moving after eleven years to become Head of Forensic Psychology at Arnold Lodge Secure Unit in Leicester (1983).
He then became the Head of Psychology at St Andrew's Healthcare Northampton in 1985, a national resource for patients requiring specialist input.In his early career he was known for being the first psychologist professionally employed in top flight English football, and one of a handful of psychologists involved in the aftermath of the Piper Alpha disaster.
William Davies, along with John Gardner, also became the first professional psychologists in English top flight football when Sir Bobby Robson employed them as consultants in 1981 at Ipswich Town F.C.
(At the time both teams included England internationals in Mick Mills, Terry Butcher and Paul Mariner for Ipswich, and John Barnes and Luther Blissett for Watford.)
In the late 1980s, Davies was one of a handful of psychologists and psychiatrists heavily involved over a two-year period in seeing many of the survivors of the Piper Alpha oil rig disaster, mainly for assessing and quantifying any post-traumatic stress disorder.