My aunt, Margery Mason, who has died aged 100, was an actor, writer and theatre manager. She was a founder member of the Actors' Company and made appearances in diverse productions, from Midsomer Murders to a Harry Potter film.

Born and brought up in Hackney, east London, she came from a modest background, and after rudimentary education left school at 15. Her parents ran a semi-professional dramatic company, from which Margery's acting career developed. Initially she performed in their company at working men's clubs in the East End of London, starting as principal boy in pantos, then succeeding to adult parts, sometimes competing with her mother for the starring female roles. Her father ran an early cinema, the Hackney Bioscope, and subsequently established the Impartial Film Report, which distributed weekly film reviews to the then many independent cinemas. Margery attended film trade showings, wrote reviews and helped produce the Report.

Before the second world war she was active in repertory theatres in Macclesfield, Oldham, and Worthing. In 1943 Ensa (the Entertainments National Service Association) recruited her for tours in Egypt, Palestine and Jordan; then again to India, Macau, Hong Kong, Singapore, Malaysia and Thailand. She was an army lieutenant, and claimed to enjoy the luxury of service life.

After the war, she returned to repertory acting and wrote her first play, And Use of Kitchen, about London bedsit life. From the 1950s to early 60s she managed theatres, including at Amersham, and later ran her own theatre company in Bangor, Northern Ireland. She was a founder-member of the Actors' Company, before joining the Royal Shakespeare Company for touring and Stratford seasons. Her marriage in 1951 to the classical violinist Peter Daminoff was short-lived.

In Talking to a Stranger, John Hopkins' 1966 seminal four-part television drama, Margery co-starred alongside Maurice Denham, Judi Dench and Michael Bryant, and gave an acclaimed performance in the final episode's central role. Other television work followed in several episodes of Peak Practice, A Family at War and The Bill, with guest appearances in Midsomer Murders, Jonathan Creek, Cadfael and many others. In films she played in The Princess Bride and had cameo parts in Love Actually and Harry Potter and Goblet of Fire.

Margery had extraordinary energy and enthusiasm. She loved travel and had been a keen horsewoman and tennis player. Until she was 99 she swam five times a week at the Swiss Cottage baths. She was an autodidact and an idealist, and loved life. She always spoke her mind and relished argument. Politically she was of the old Left, and for many years was a member of the Communist party. She resigned in disgust after the Soviet invasion of Czechoslovakia.

Her chief love was theatre and the spoken word: poetry, novels, plays. Her farewell to the stage came in 2003 when, aged 90, she played the nurse in Chekhov's Three Sisters at the Playhouse theatre, London.