The English native P.H. Moriarty began acting late in life, having worked for many years in other professions, including as a boxer and a longshoresman. While a film crew was shooting a scene on the English docks one day, the production crew discovered Moriarty working there, and they asked him to act in the film. Thus began his acting career.
Moriarty's film credits include Guy Ritchie's feature film Lock, Stock and Two Smoking Barrels (1998), in which he starred as Hatchet Harry. Moriarty also has had parts in Chaplin (1992), Patriot Games (1992), Jaws 3-D (1983), The Long Good Friday (1980) and the Western-inspired sci-fi film Outland (1981). He also has starred in various British television programs.