‘It is my freedom from English convention,’ James Joyce wrote to his brother, ‘which lies at the source of my talent.’ The Irish novel was never hamstrung by the need for shapely plots and well-rounded characters. Instead, like postcolonial literatures today, it was a place for experiment and innovation. Estranged from the metropolitan culture, Irish writers made it up as they went along, cobbling together bits and pieces of other people’s traditions to compensate for the fact that they lacked a canonical literary heritage of their own. From Swift’s Gulliver’s Travels to Bram Stoker’s Dracula, bending the rules of realism is as Irish as emigration. Almost a century ago, Ireland was the only region of the United Kingdom to produce a native modernist art. Its fascination with verbal play and extravagance, which runs as far back as the early middle ages, sat well with the modernist adventure. So did its sense of history as dark and fragmented.

Joseph O’Connor’s magnificent new novel, Redemption Falls, falls squarely in this great non-tradition. It is a huge dishevelled monster of a book, crammed with all manner of typographical stunts. The text is stuffed with posters, verses, letters, doodles, extracts from notebooks and newspapers, snatches of ballads, transcripts of documents and stories within stories. This, too, has a venerable Irish pedigree. From Laurence Sterne to Joyce, literary experiment by Irish writers often includes playing around with the book itself as a material object. In an intensely oral culture, there is bound to be something rather perplexing about print. How can these little black marks on a page actually be meaningful?

Set in the US during the civil war, Redemption Falls is as richly digressive a narrative as Ulysses or Finnegans Wake. We follow the fortunes of the Irish immigrant Eliza Mooney, stumbling across war-torn America in search of her brother Jeremiah, whom the war has sucked in as a drummer boy. But this particular narrative weaves its way in and out of half a dozen others, and at the centre of the whole tangled web of tales stands the epic figure of orator, soldier and philanderer James O’Keefe. A fast-living Irish republican who as a young man saw infants starve on the quays of his native Waterford, O’Keefe has served time as a felon in Van Diemen’s Land, and made his escape from those ‘hope-scalded rocks’ to the US. He turns up as a celebrity lecturer in New York, marries a Latino aristocrat and settles for a while in a grand house in Manhattan (‘Fifth Avenue Fenianism’, as the narrator remarks). Famed as O’Keefe the Blade, he fights bravely with the Yankee forces but can’t resist striking a superior officer and is stripped of his rank. He also works his way through a string of exotic mistresses and ends up as governor of the southern town of Redemption Falls, with a death sentence for grand larceny and general anarchy on his head. With his customary flair for enraging the authorities, he petitions the US Congress to change the name of the town to Dublin City.

Irish writers may have bent the rules of realism, but the joke is that O’Keefe is not so improbable a figure. Several of the anti-colonial Young Irelanders on whom he is based had almost equally flamboyant careers. In his wanderings around the globe, he proves that if the Irish are a cosmopolitan race, they have the British to thank for it. Redemption Falls is full of hybridity and miscegenation, mixed tongues and cross-bred identities. Jeremiah O’Moody’s accent is a blend of Louisiana twang and Irish brogue, and the novel itself brims with a Babel of idioms, from African-American to high-class Manhattan. It is a gloriously polyphonic work, full of overlapping voices and clashing dialects. O’Keefe himself translates a Scottish song into Gaelic, then Italian and then courtly French, in a microcosm of his author’s own multi-tongued eloquence.

Too much modern fiction is verbally colourless. In Ireland, however, language has always been more self-conscious, given that most of its writers use a kind of speech that, historically speaking, is not their own. It is hard for language to appear innocent when it has been a political minefield for centuries. Redemption Falls perpetrates hardly one slack or unsculptured sentence for the whole of its 450 pages. Like Joyce, O’Connor combines his panoramic range with a close eye to the grain and texture of the phrase. Eliza Mooney is a ‘cadaverous madwoman in her ash-dusted rags, who leaves footprints of blood … whose face looks as though it has been forced through a mangle before being sutured back on to her skull’.

There are times when this lapses into manic self-parody: ‘They roosted up the masts dropping guano on the famished, and the faithful are wading in faeryshite yet: they were gusted across the billows by the reeking breath above them as it roared the oratorios of vengeance.’ This sounds like a mixture of blarney and Dylan Thomas on a bad day. Yet the lapses are remarkably rare. Redemption Falls is a major work of modern fiction from an astonishingly accomplished writer.