When Granville Barker died in 1946 at the age of 68, the nonagenarian Shaw described him as “altogether the most distinguished and incomparably the most cultivated person whom circumstances had driven into the theatre at that time”, meaning the early 20th century. That was a generous tribute - since the red-headed Barker had cruelly rejected the red-headed dramatist, who had been widely, if wrongly, rumoured to be his literal as well as his theatrical father - but nothing less than the truth.

Samuel West's impending revival of his Waste at the Almeida should help to confirm that truth. Certainly Barker was as near to a Renaissance man as the British stage has produced. He was a brilliant dramatist, a bold impresario, a pioneering director, an articulate theoretician, a crusader for theatrical change and the actor who created many Shavian characters, among them Tanner in Man and Superman. And when he ditched his actress wife, Lillah McCarthy, for an American heiress who hated Shaw, the stage and her husband's political radicalism, Barker reinvented himself as the scholar whose Prefaces to Shakespeare are still worth reading.

The fate of Waste in 1907 also helped to alienate him from a British theatre whose inadequacies he persistently attacked. The protagonist is a politician whose career is ruined when the woman with whom he's had a casual fling dies after ending her pregnancy. But the idea of abortion was as much anathema to the censor as the play's cynical portrait of contemporary politics, and Waste received only a private reading, at which Shaw, H.G. Wells and a devastated Barker took some of the roles.

No fewer than 71 writers, among them Yeats, James and Conrad, signed a letter to The Times protesting at the ban; but our theatre critic at the time, though calling Waste “a work of extraordinary power and unflinching truthfulness”, decided that its very authenticity made it unfit for public performance. But at least Barker was inspired to become as active in the war against stage censorship as he was in another battle that wasn't to see success until the 1960s: the fight for a national theatre.

Barker didn't just proselytise powerfully for a subsidised, non-profit-making theatre that would “deliver us from managers with wooden heads” and stage the world's best plays in rep. Starting in 1904, he proved the idea viable at the Royal Court and, later, other theatres. He put Shaw definitively on the map with a succession of premieres of his work, among them a production of John Bull's Other Island at which Edward VII laughed so much that he broke his chair. He rediscovered Euripides, transformed the novelist Galsworthy into a major dramatist, and, not least, staged his own plays.

Much of his work seemed super-subtle and overintellectual at the time. Somerset Maugham, for instance, thought it needed “more force, more go, more guts, more beef”. But in our era the RSC has rehabilitated The Marrying of Ann Leete, with Mia Farrow playing the aristocratic girl who rejects privileged suitors for her father's gardener, and the National has done the same for The Madras House, casting Paul Scofield as a Muslim convert highly critical of Europe's attitude to its females.

That play has as much to say about the predicament of women as Barker's The Voysey Inheritance, which involves a legal firm that has been fleecing its clients, has about money or Waste about politics. All display a large-mindedness unmatched in the period by anyone but Shaw. And Voysey in particular leaves me feeling that Barker was the Edwardian period's supreme dramatist: a bit discursive but always incisive and, given good actors, always gripping.

But then Barker was supreme in everything he touched. He was in effect the British Stanislavsky, more or less introducing the art of direction to the nation and becoming renowned for his respect for texts, attention to detail, understanding of actors and love of spare, clear staging. One result was a production of Galsworthy's Justice that so moved the Home Secretary Winston Churchill that he ended the practice of putting newly convicted prisoners into solitary. Barker could even be said to be the spiritual father of the RSC.

Yet the actor Lewis Casson spoke for many when he wrote that Barker “threw off the dust of battle and became a mere professor”. The once-penniless son of a property speculator changed his name to Harley Granville-Barker, hired liveried footmen and abandoned the live theatre. Not that this made him happy. In almost all his plays there's an intelligent, emotionally aloof, morally troubled character painfully aware of his own limitations, and Barker was very like that. “I feel my life is useless” were virtually his last words. How one wishes one could dig him up and tell him he was a genuinely great man.

Waste opens at the Almeida, N1 (020-7359 4404), on Thurs (www.almeida.co.uk)

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