He worked regularly as a voice actor, and was known for many years as "The Man in Black", the narrator of the BBC Radio horror series Appointment with Fear.

He was the son of the actor Franklin Dyall and the actress and author Mary Phyllis Joan Logan, who acted and wrote as Concordia Merrel.

In the same year he had a small role as a German officer in The Life and Death of Colonel Blimp and, the following year, played the Duke of Burgundy in Laurence Olivier's film version of Henry V. In 1946, he appeared, uncredited, as the character Stephen Lynn in the romantic film drama Brief Encounter; Lynn is protagonist Alec Harvey's friend whose unexpected arrival spoils Alec's opportunity of consummating his romance.

In the same year he voiced the character of evil mastermind Dr. Noah in the James Bond parody film Casino Royale; as well as the unseen God in Faust Legend-inspired comedy Bedazzled, for which he was uncredited.

He was in the cast of the BBC's Doctor Who to portray the Black Guardian in several serials (The Armageddon Factor from 1979 and the Mawdryn Undead / Terminus / Enlightenment trilogy in 1983).