Dignam was born on the 20th March 1909, the son of salesman in the steel industry in Sheffield.
He was educated at the Jesuit College where he appeared in numerous Shakespearean plays.
Although his first plan was to become a journalist, he tried his luck at professional acting as early as 1929 with Phillip ben Greet's Shakespeare touring company. He became one of the first members of Equity, the actors' union, founded that very year. Very soon afterwards, he joined the Communist Party, in which he remained until death.
In the Thirties, he played in the West End, opened a rep in Croydon, and was at the Old Vic.
Three years’ war service ensued, until he was wounded at Anzio. Dignam was a keen supporter of Unity Theatre.
A superb supporting actor, he payed Buckingham, Claudius, Malvolio, Polonius, and such alongside the leading stars of stage and screen.
In films, Dignam was the Laird in `The Maggie' (1954), the prosecuting attorney in `Carrington, V.C.' (1955), and Merlin in Cornel Wilde's `Sword of Lancelot' (1962) and many other movies.
His wife, Virginia, the poet Ginny Lewis, was for a long time the film critic of the Morning Star and its predecessor.
Mark Dignam was in employment as a professional actor until the year he died on the 29th September 1989.