While politics and journalism claimed more of his time than academe, his scholarly preoccupation with Edmund Burke grew with time, and kept pace with his own odyssey from the Left. The Great Melody: A thematic biography of Edmund Burke (Sinclair-Stevenson) appeared in 1992 as the final instalment of a process that had begun with his seminal introduction to the 1968 Penguin Classic edition of Reflections on the Revolution in France. It is impossible not to sense O'Brien's emotional identification with his subject's idiosyncratic Irishness, his Catholic background, his political progress, and his wish to command a world stage; the first person singular intrudes far more persistently than in most biographies. By the time he wrote it in The Great Melody, O'Brien fully identified with Philippe Raynaud's definition of Burke's stance regarding the Revolution: "à la fois libérale et contre-révolutionnaire." This identification unbalances the book's structure at some points, and allows obsessive reiteration; it also enhances it as an instalment of intellectual autobiography. The epilogue, placing French and Russian revolutions in direct line, shows how far O'Brien had travelled from the marxisant fashions of his youth. But the achievement of the book is to unite the "liberal" Burke (on India, America, Ireland) with the "counter-revolutionary" Burke on the totalitarianisms bred by abstract theory. In some ways it reads like an anticipation of the Memoir (Profile Books, 1998) of his own life he published a few years later.

If The Great Melody is O'Brien's major academic work, States of Ireland is the one that will endure as a vital moment in Irish intellectual and political history. In the many memorial articles written after his death last December, several of the writers recalled reading it as an epiphanic moment. Such people included Ulster Unionists who suddenly saw "the South" in a different light, and at least one IRA member who began silently to question the verities of the republican cause. It also made the SDLP leader John Hume an enemy for life, and precipitated a motion within the Irish Labour party to expel O'Brien from their membership. It remains a book that should be read at regular intervals by anyone trying to understand Irish history. O'Brien described it as "an enquiry into certain aspects of Irish history, consciousness and society", and it anticipated several of his later books in treating history autobiographically - beginning with his grandfather's reaction to the Parnell Split of 1890-91, and going on to evoke the mind-set of that Home Rule generation on the brink of unforeseen revolution.

The tribal assumptions, class attitudes and confessional undercurrents of the era supply one level of the commentary. On another, he deconstructs James Connolly's Marxist critique of Irish history (which ignored the implications of 19th-century Belfast industrialisation), relishes Eamonn de Valera's serpentine strategies, and provides some toothsome autobiographical detail about his own work in the Department of External Affairs, particularly as Frank Aiken's emissary to the Catholic communities of Northern Ireland. On one occasion, in 1952, he travels with an English Jesuit observer, Father Wingfield-Digby, who is shown the electoral map of Derry by a local Catholic politician, Senator Lennon.