Some years ago Seamus Deane described the work of fellow poet, critic and Field Day director Tom Paulin as "the poetry of commitment". It is a perceptive comment. Commitment shapes Paulin's level of engagement with whatever subject he addresses; whether it is literature, the chaotic politics of Northern Ireland or merely trying to restart the stalled motor of his small boat while at sea. However, it is ironic that neither his poetry nor his criticism nor his adroit versions of Greek drama have made him as famous as his appearances on BBC 2's The Late Review. No, not even his superb new book about William Hazlitt's prose will match the following Paulin's television performances have earned him.

Just as the visual image appears to have taken control of culture, critical opinion is now dominated by the sound bite. Televised debate, be it about politics, football or the latest film releases, is both exciting and influential. Long before The Late Review had acquired its cult status, Paulin had already emerged as a singular television performer, having already impressed with radio broadcasts about poetry. Over several seasons, both he and Germaine Greer had proved entertainingly iconoclastic on televised Booker Prize presentation nights, debating - or in most instances - dismissing the merits of the contenders.

While Greer's irritation soared to eloquent hysteria, Paulin's approach tended towards a pained bewilderment invariably undercut by astute observation. In addition to his distinctive accent, pale eyes and intriguing range of facial expressions, offering an array of creases and crevices which may be summoned to his face at will, Paulin accompanies his remarks with shrugs and exasperated hand gestures and mastery of the pause - small wonder viewers remember him. Not surprisingly the pair were destined to be recruited for a regular slot.

Paulin likens the programme which is trendy, topical and intimidatingly "clever" to participating in a "fast seminar". Few television performers can call on the gentle, almost fey, vagueness of delivery combined with intellectual aggression Paulin has at his resources. Speaking at the annual Synge Summer School in Rathdrum, Co Wicklow in 1993, he offered a dreamy, inspirational and carefully directed interpretation of Riders To The Sea. More recently he addressed the Hewitt Summer School on the subject of Hazlitt, and characteristically gave the impression of simultaneously having just been struck by a thought while clearly long knowing it by heart. It is his singularly individual way of injecting passion and responsibility into the business of textual criticism.

These qualities are present throughout his new book. For him Hazlitt is "the most allusive of essayists" and he is conscious of Hazlitt's lost reputation and that somehow almost all of the books and essays written by this pioneering master of English prose are now out of print. "That Hazlitt is so tenuously lodged in the cultural memory at the present time," he laments, "is saddening. Few readers - and still fewer places - claim him."

Paulin's excellent study not only examines Hazlitt's "ecstatically definite prose" and classical base, it places it within a cultural context, of its time and more specifically within that of Unitarianism as a remarkable intellectual tradition. It is no coincidence. As he remarks: "The book actually started out as a study of Unitarianism, but I soon realised it is too big a subject." It is a fortunate decision, by focusing on Hazlitt, "perhaps the only critic in English to invest his vast, complex aesthetic terminology with a Shakespearean richness", Paulin has achieved a masterwork of literary reclamation. Few books published this year are likely to be more important, fewer still may be as good. A crafted, thinking, vivid study, it is unique, it is different.

Obviously pleased with the book, Paulin casually remarks: "It'll only sell a few copies, people don't tend to read literary books." Of the many reasons for reading it, however, is that Paulin has deliberately avoided the now standard practice of producing biographies about writers which occasionally nod to the work while choosing to concentrate on the life.

And Hazlitt's personal life is a sad, messy story which includes two failed marriages as well as an ill-advised obsession with a young woman, who rejected Hazlitt, leaving him to write Liber Amoris (1823), a self-exposing account of the relationship. Hazlitt died penniless in a Soho lodging house in 1830, with his only son, William, and essayist Charles Lamb at his bedside.

Many unflattering descriptions testify to Hazlitt's unhappy personality. Paulin, though stressing "the seemingly willed chaos of his personal life" in the creating of his quicksilver genius, is mainly concerned with the imagination and intellect which shaped the prose. "Although Hazlitt had no religious belief, and was critical of certain Protestant faults - aridity, meanness of spirit, lack of imagination - he identified in moments of crisis with Unitarian values, and more widely with Dissenting Protestantism."

It is a half-heartedly sunny Saturday afternoon in Galway. Paulin is in Ireland to participate at the Cuirt Festival of Literature. Before he appears for the interview, a man, having heard Paulin's name being mentioned by the hotel receptionist who has announced "he is on his way", decides to wait. When Paulin appears, the man tells him he is a fan, always watches him on The Late Review and asks him has he ever written anything? Paulin is very polite and quite shy and mentions he has just finished a book and is feeling "written out". The man then mentions having just written a poem inspired by a train journey and suggests Paulin do likewise; take a train and clear his head. Mentioning the possibilities of flying over Ireland, Paulin thanks him for the advice and sets off looking for a quiet place to talk.

Nervy and slightly weary, he appears much as he does on television. Looking around him at the busy street scene, he says, "I've always liked Galway". Adding to the traffic sounds is the commentary of that afternoon's big rugby match, the All Ireland league final between Garryowen and Shannon. The commentary seems to be following us. Finding that "quiet place to talk" develops into a quest.

Unlike many readers, Paulin's interest in Hazlitt did not begin at school. He didn't first read Hazlitt's famous essay "The Fight" as a schoolboy. "We were taught Orwell and Swift, I didn't read Hazlitt until much later." For him, Hazlitt, who was born in Kent in 1778 of an Irish Unitarian father and an English mother from a Dissenting family, personifies the great liberal Dissenting tradition. Paulin points out that it is easy to see Unitarianism as simply a form of liberal humanism retaining elements of Christianity, but it is primarily a culture with a principled faith in God and has been shaped by a historical memory of martyrdom and suffering. It is a tradition which continues to interest Paulin.

In his chapter "Northern Protestant Oratory and Writing 1791-1985", from The Field Day Anthology of Irish Writing (1991), Paulin traces the tradition from William Drennan to Harold McCusker. Paulin acknowledges the dialogical or polemical nature of the Protestant imagination, an imagination that sees itself dramatically as pitched against certain powerful ideas that threaten its existence and values. "Feisty, restless, argumentative, never quite at home in this world, that imagination has shaped itself in traditionally aesthetic form in the North of Ireland. There, its characteristic forms of cultural production are the sermon, the pamphlet, the political speech." Explaining his choice of material, Paulin points out that his selection of Protestant ecriture is intended as an "enabling initiative, rather than as a canonical gathering of isolated texts".

That last sentence is also very true of his approach to merging text and opinion. Paulin's reading of Hazlitt's life - and, more importantly, Hazlitt's world - is reasoned, lively and convincingly argued. It is also very logical. Even passing comments - such as "The year 1798 has left few traces in the English historical memory, but in Ireland it is shorthand for an attempt to establish a united, indivisible republic" - are weighted. Many of the observations are so deft: "What draws Hazlitt so strongly to Burke's style is its quality of excess, its dangerous wildness, its brilliant fancy."

The fact that Hazlitt's father, the Rev William Hazlitt, was from Co Tipperary has certainly been lost. And Paulin refers to a journal entry made by Margaret Hazlitt, suggesting that had the family remained in Co Cork where the Rev William was minister at Bandon from 1780-83, he would not have survived the 1798 rebellion. Perhaps Hazlitt's Irishness counters the potentially Arnoldian tone of Hazlitt's saying the Irish "have wit, genius, eloquence, imagination, affections: but they want coherence of understanding, and consequently have no standard of thought or action. . . their animal spirits run away with them: their reason is a jade. . . they are a wild people." Hazlitt senior was known for his outspokenness and "never disguised his sentiments". Shades of his son's difficult temperament were hinted at by his father's fearless behaviour. With the ending of the American War of Independence in 1783, the family set off for the US and stayed there for four years. While there the Rev Hazlitt established the first Unitarian church in Boston. More than a century later the family of poet T.S. Eliot would worship there.

Paulin's book not only examines the extraordinary genius of Hazlitt, who elevated journalism to an art, but he is also exploring in wider terms the notion of the critic; the critic as actor, performer and as artist. Hazlitt wrote about many things. Initially a painter, he remained interested in the visual arts throughout his life, as evident from his wonderful pieces on Hogarth and Poussin. Hazlitt's "On a Landscape of Nicolas Poussin" contains, according to Paulin, one of the finest opening paragraphs in the history of criticism, "a paragraph so long and carefuly moulded, so epic in its momentum, that it is a concentrated essay in itself". His hero was Napoleon and his pet obsession was Burke, whose prose style he greatly admired. Both were from mixed Irish/English parentage. "The problem for Hazlitt," explains Paulin, "is that Burke was both a great prose stylist and a monarchist. Hazlitt wants somehow to reconcile an admiration of his style with a detestation he feels for Burke's politics."

From his first reading of Burke when he was 18 - in the same year he met Coleridge - Hazlitt began a lifelong, even obsessive intellectual relationship with a writer whose defection to the Tory cause was mourned by the Dissenters, whose civil rights he had championed. Like Milton and Shakespeare, Burke is part of the deep structure of Hazlitt's critical imagination, but, because of their shared Irish background, he is even more personally part of his soul and identity."

One of three sons, Tom Paulin was born in Leeds in 1949. His father was teaching there at the time. On becoming the headmaster of Annadale Grammar School, he moved the family to Belfast where the young Paulin, then four, was to grow up in an atmosphere of liberal Protestantism. As a boy, he says, he was not particularly aware of the differences or divisions between Protestants and Catholics. Having been born in England and educated at the universities of Hull and Oxford - the latter is where he now teaches - does he consider himself Irish or English? "I feel bits and pieces," he says vaguely, "but yes I would, I do, feel more Irish than anything else."

Asking him about his early life appears to surprise him. Now the father of two teenage sons, he seems more engaged with the present. He doesn't romanticise his past. He admits it was "slightly awkward" being a pupil at the school his headmaster father presided over, "but that didn't last long".

Every summer, for more than 40 years now, Paulin has gone to Portnoo, a tiny fishing village in north-west Donegal. There he "messes about" with his boat. Last year, during a chance encounter, he looked so much at home as a barefoot fisherman, albeit one without any fish, that I assumed he was the boat man arriving to take us out to a island unreachable at high tide. Dismissing any notion that he is particularly outdoorish, Paulin says "I was never good at sport but I enjoy being there".

One of his brothers died in his early 20s. How did this affect him? Still wearing his habitual expression of bewildered concern, Paulin answers honestly: "I don't really know how it affected me. I'm sure it did. But I don't know." As a schoolboy he remembers reading Seamus Heaney's first collection, Death Of A Naturalist, in 1966. In common with Paul Muldoon, three years his junior, Paulin belongs to the generation of Ulster poets which followed Heaney, Michael Longley and Derek Mahon. Asked about the dominance of major poets from the North, he seems quite non-committal. The civil rights movement had begun to assert itself during his late teens. But Paulin is reluctant to be drawn into making big statements about Northern Ireland. Hopeful that change is on the way, he wishes to say nothing that may appear provocative.

On leaving school, he went to Hull University to study English. At Hull he met his wife Giti, from a Catholic Indian family, who grew up in Strabane. "We only found out a few years ago when we were speaking with Felim Egan [the painter] that they had grown up yards from each other." He is still struck by the coincidence. Paulin's years there coincided with Phillip Larkin's tenure as librarian at Hull. Why didn't Paulin attend Queen's? "I don't know. I suppose it was my generation. The late 1960s, I don't know. We were all filled, fired with the idea that you were supposed to go away, to see other places." While at Hull, he began writing poetry. He has published several collections: A State Of Justice, The Strange Museum, Liberty Tree, Fivemiletown and most recently, Walking A Line. He says he enjoys commissions and likes writing to deadlines.

Admitting to never reading new fiction unless he has to review it, Paulin leaves one feeling that he sees the act of criticism at times to be more important than the actual work under scrutiny. "Well, I don't think that, but it is true that popular culture is of the moment and it is important." Paulin's essays and criticism which include a study of Thomas Hardy, The Poetry Of Perception, and now this wonderful book, suggest that he, in an age of few great critics, is certainly a fine one. His television self may have overtaken his writer self, but Paulin does not seem bothered by it. Having taught at Nottingham University, he is currently the G.M. Young Lecturer at Hertford College, Oxford.

Unlike many poets, he seems content to downplay it. Far from consciously playing the poet, he says: "I don't sit about thinking of poetry, I tend to wait for a poem to happen."

The Day-Star Of Liberty - William Hazlitt's Radical Style by Tom Paulin will be published by Faber on June 8th, price £22.50.