Hartnoll herself wrote all the references to the French theatre and it is significant that amongst the many other contributors were Sybil Rosenfeld, Ifan Kyrle Fletcher, Richard Southern, Muriel St Clare Byrne, George Speaight - all fellow founder members of the Society for Theatre Research in 1948. The Companion became an OUP bestseller with a reprint in 1952, a second edition in 1957, further reprints and a third edition, largely revised, in 1967. It still features in the publisher's list and is accepted as the standard reference work in the field.
Born in Egypt in 1906, the daughter of an army officer, Hartnoll was sent to England in childhood to stay with relatives and to be educated at St Mary's Convent, Wantage, Cheltenham Ladies College, and finally St Hugh's College, Oxford, where she read English. She continued her studies at the Universities of Lyons and Algiers .
She worked briefly in Blackwell's Bookshop in Oxford and as a secretary in a girls' school in Jerusalem, and then, from 1929 to 1967, was employed as a reader, translator and editor by the publishing house of Macmillan. With a firm grounding in Latin and Greek she had a fluent facility for language, being trilingual in English, French and German, and able to converse in Italian, Swedish, Hebrew and Arabic.
Poetry was an interest which continued throughout her life. She had won the Newdigate Prize at Oxford in 1929, and the Oxford Prize for Sacred Verse in 1947 and 1965. Her passion, however, was for the theatre and in theatre history, a subject which she taught in the 1950s at the Royal Academy of Dramatic Art. She served on the committee of the Society for Theatre Research for many years. She was also a founder member of the International Federation for Theatre Research and one of the early editors of its journal, Theatre Research/Recherches Theatrales.
Although the re-editing and revising of the Companion was a lifelong occupation, she also produced A Concise Companion in 1979, A Concise History of the Theatre in 1968 and several other works such as Plays and Players (1984) and Who's Who in Shaw (1975). She assisted John Gielgud, who became a close friend, in the editing of his mother's early theatrical criticism.
On her retirement to Lyme Regis she wrote plays for the local dramatic society - The Swedenheims and Peter Peppercorn, as well as an adaptation of George Colman's The Jealous Wife. There was one novel - The Grecian Enchanted (1952).
Phyllis Hartnoll had an energy and a gift for the encouragement of others in a self-effacing, supportive way, and for the general good. She was also generously hospitable and enjoyed an active social life. She had a formidable zest for work and an ability to concentrate her considerable organisational skills towards the achievement of a target. This was the more remarkable in view of her continuing battle against illness which shadowed her life from the typhoid contracted in childhood in Egypt.
She is survived by her companion of many years, Winifred Kimberley.
Phyllis Hartnoll, theatre historian: born 22 September 1906; died Lyme Regis 8 January 1997.