The play, Not About Nightingales, was written in the Thirties when Williams, who died in 1983, was in his twenties. It would have been one of the earliest plays he wrote. Set in a men's prison, it partly concerns homosexual relationships. That is the probable reason why American publishers and theatre managements were wary of the work.
It has never been staged. Nor does it appear in any collections by the author of A Streetcar Named Desire, Cat On a Hot Tin Roof and The Glass Menagerie.
Vanessa Redgrave came across a reference to the play in a new biography about the young Tennessee Williams. She became intrigued and went to New York to urge Williams's long time friend Maria St Juste, who managed his estate, to release the manuscript.
Maria St Juste, who has since died, had never released the play because she felt that if Williams had not released it in his lifetime he must have had his reasons. However, Ms Redgrave and she had been friends for some time and she agreed to release it to her. The annotated typescript was found among the late playwright's papers, and Ms Redgrave secured the rights for its performance.
The one misfortune for her is that the main female part is a 19-year- old secretary, which she is too old to play. The one middle-aged woman in the play appears only for a brief scene. Nevertheless, she was keen to play that role, until Trevor Nunn, the director designate of the National Theatre told her it would be inappropriate for her to take such a small role.
Announcing the discovery yesterday, Nunn said: "It is pretty extraordinary for someone to be talking about the world premiere of a new Tennessee Williams play. That should be an impossibility. But it was discovered by Vanessa who was intrepid and resolute and got hold of a copy which was a typescript.
"It's never been done, never been read. It is completely unknown.
"It is a complete play and a very harrowing play. It has elements of the style which you would associate with Tennessee Williams, but is not really like a Tennessee Williams play. It is about a young prisoner who has a poetic sense of himself and what he wants to achieve ...
"It's fantastically bad luck for Vanessa that the only substantial woman's part is of a 19-year old-secretary."
The production will though be a co-production with the company run by Vanessa Redgrave and her brother Corin.