Sean O’Casey was an Irish playwright famous for his Dublin trilogy The Plough and the Stars, Juno and the Paycock, and The Shadow of a Gunman.

On the rare occasions when they were part of the A’ level English literature syllabus in schools, they were taught as tragic comedies or farce. They were almost always devoid of historical, political and even literary context.

As the title of Paul O’Brien’s magnificent new book, politics was a central part of O’Casey’s life. He was an activist in the workers’ movement in Dublin in the early 20th century, a staunch member of James Larkin’s Irish Transport and General Workers Union (ITGWU).

O’Casey became secretary of James Connolly’s Irish Citizens Army, founded to defend workers from attack during the Dublin lock-out of 1913. He was also a prodigious writer of letters and autobiographies, as well as plays.

O’Brien’s thematic structure, rather than a linear biographical approach, helps to explore all these strands. Although he has written a sympathetic account of O’Casey, it explores the many contradictions and complexities of both the man and his literary output.

It is immensely scholarly and exhaustively researched, but never dry. Here was a working class playwright who ruffled the feathers of a conservative establishment. They wanted to hold on to the fictional notion of a romantic Gaelic culture, unsullied by the experiences of the Irish working class.

O’Brien argues that O’Casey was uniquely placed to write about the working class. “Almost alone of his literary generation, his background in the north Dublin tenements gave him access to that world,” he writes.

This authenticity is epitomised by the way he gave voice to the language and dialects of Dublin workers, whether they were expressing tragedy or humour. Drama, with spoken interaction between characters, was central to this. On the written page it may read as clumsy and hackneyed, a poor reflection of living speech. On the stage, it combines lyricism with authenticity.

Class politics was central to O’Casey. The 1913 Dublin Lockout was a transformative event, and his relationship with Larkin shaped his political outlook.

But in the years that followed, there was a growing tension between working class politics and the fight against British rule of Ireland. This tension culminated in a famous falling-out with Connolly, which led to O’Casey’s resignation from the Irish Citizen Army. At its heart was O’Casey’s failure to understand the link between the anti-imperialist struggle of Irish nationalists and the socialist and labour movement.

After the defeat of the lockout and the advent of the First World War, he launched an intemperate attack on Connolly. Connolly had tried to build a united front with the nationalists in the Irish Volunteers against the imperialist war and to oppose conscription to the British Army.

O’Casey argued that under Connolly’s leadership, the ITGWU’s headquarters was “no longer the headquarters of the Irish labour movement but the centre of Irish national disaffection”. The red flag had been usurped by the green, he argued. He opposed Connolly’s alliance with the Irish Volunteers—and the Citizen Army’s participation in the Easter Rising against British rule in 1916.

Connolly saw the links between workers’ struggle and the fight against imperialism. Capitalism had imposed a system of private land ownership in Ireland, which led to the development of the landlord-tenant system of tenure. At the same time, British colonialism had held back capitalist development in Ireland, and so the growth of the urban working class.

O’Casey had no grasp of the revolutionary dynamic that led up to 1916. He created a false polarisation between Larkin and Connolly—to the detriment of the latter. O’Brien characterises him as “a disgruntled outsider, a hurler on the ditch, shouting the odds as history passed him by”.

But he did keep in touch with his former comrades who took part in the Easter Rising and was concerned for their welfare. He was also prominent in his support for those who subsequently were jailed.

Literary critics have suggested that he suffered from “survivors’ guilt” because he failed to take part in the Easter Rising. And so, they argue, he reflected that in the way he portrayed the rising’s participants in The Plough and the Stars.

My own view is that this misses the point of one of O’Casey’s greatest literary strengths. His determination to look sceptically and satirise the participants is an antidote to the romantic mythologising of the rising, and the conservative Irish state’s appropriation of its memory.

This is carried over into his more experimental later plays, such as Cock a Doodle Dandy and The Drums of Father Ned. Here, he lampoons an Ireland in thrall to the Church and dodgy businessmen. Workers are trapped between their fight for better pay and conditions and their subservience to those who wanted to deny them any prospect of economic or social advancement.

O’Casey’s socialism was shaped and distorted illusions in Stalinist Russia. He retained an affection for Stalin’s Russia despite the counter revolution and the betrayal of the 1917 Russian Revolution. Even in the 1930s he described Moscow as “a flame to light the way of all men towards the people’s ownership of the world”. Unlike many of his generation, he stuck with the Soviet Union after the suppression of the Hungarian Revolution of 1956.

But do his political flaws cancel his political and artistic commitment? O’Brien cites the assessment of Patrick Galvin, part of a new breed of Irish activists. “You took O’Casey as he was, warts and all, or you left him alone,” he says. “The wonder of it is that he managed superbly well to survive the attentions of his friends and the wishes of his enemies.

“No Irish writer of my generation can repay the debt we owe to O’Casey. He kept the flag flying against Church and State for longer than most of us can remember. And although he wasn’t always right, by intention he was never wrong.”

These sentiments were echoed by his fellow writer and exile Samuel Beckett. “To my great compatriot Sean O’Casey from France where he is honoured, I send my enduring gratitude and homage,” he said.

O’Casey’s plays represented strong women characters, often as a counterpoint to feckless male ones. This quality was carried over into real life with his championing of women’s rights.

O’Casey’s daughter Shivaun provides a supportive endorsement of O’Brien’s book. She recalls, “He was aware of the crippling dominance of the Catholic church and the dreadful number of young girls who had to come to England for abortions. He thought that abortion should be the woman’s decision and health and schools should be free.”

O’Brien addresses the more neglected aspects of O’Casey’s literary output—his six-volume autobiography and his 2,500 letters—with a nuanced assessment. He responds to the many critics of the autobiography by insisting that it should be read for its insights and literary quality, rather than its historical accuracy.

I would recommend this book wholeheartedly to all those interested in Irish literature, history and politics. O’Casey emerges, through all his contradictions and complexities, as a writer of the highest order who gave an eloquent voice to the Dublin working class.

Sean O’Casey—political activist and writer by Paul O’Brien. Cork University Press, £35. Book launch Fri 24 Nov, 6.30pm, Bookmarks Bookshop, 1 Bloomsbury Street London WC1B 3QE. Available from Bookmarks