After training at RADA, his theatre work included the original production of The Barretts of Wimpole Street at Malvern (1930) and its subsequent West End transfer (1930–1932).

[4] Working until shortly before his death, he appeared in nearly 90 film and television productions, where he often portrayed meek or mild-mannered types in supporting roles.

[6] Afterwards he got more film offers, including the literature adaption Kidnapped (1960) and fantasy/horror pictures like The Three Lives of Thomasina (1963), The Tomb of Ligeia (1964) and It!

[4] One of his last roles, released after his death in December 1966 at age 78, was in Chaplin's last film A Countess from Hong Kong (1967).

[7] Here Johnston portrayed an old British businessman in Hong Kong, who introduces the leading characters of Marlon Brando and Sophia Loren to each other in the opening scenes.