It was a role that Stewart was reluctant to take on. A reserved, private man with very strong views on the scholarly responsibilities of professional historians, he disliked polemic in principle. And in the Ulster of the 1970s and 1980s, such polemic could be a dangerous as well as a nasty business.
Nevertheless Tony Stewart felt compelled to take a stand. In 1977 his most famous book, The Narrow Ground; aspects of Ulster History 1609-1909, jointly won the Ewart Biggs prize. The work reflects the sense of shock experienced by an educated Ulsterman in the face of the explosion of sectarian wrath following decades of relative stability, prosperity and (under Terence O'Neill) low key liberalisation.
Stewart was impressed (and depressed) by the way in which precisely the same geographical locations which provided moments of bloody horror in earlier centuries were now presenting their symptoms again. He argued that Winston Churchill's remark about "the integrity of their quarrel" came close to defining the character of the Ulster problem. People simply inherited communal attitudes; Catholic and Protestant had no need to get to know each other better, they already knew each other too well. The success of this elegantly written book projected Stewart as the expert on the Northern Irish mindset; more particularly he was seen as having a special insight into Unionist thinking.
Those keen to find solutions for the Ulster question sought his advice, ignoring the cautious, pessimistic nature of his work. Stewart served, for example, on the second (unofficial) Kilbrandon Commission and on the committee of the British Irish Association.
The BIA in the 1980s played a significant role – by bringing together senior officials from London and Dublin at a time when this contact had a genuine novelty – in the creation of the Anglo Irish Agreement of 1985. This gave Dublin an institutionalised voice for the first time in the affairs of Northern Ireland and outraged the Unionist community. Stewart was so dismayed that he resigned from the BIA executive.
Anthony Terence Quincy Stewart was born on July 8 1929 in Belfast, where his father's family had been bakers and confectioners since the early 19th century. He was educated at Royal Belfast Academical Institution and took a first in History at Queen's University Belfast. His original intention was to start research on medieval European history, but family circumstances compelled him to drop this idea and instead take teaching jobs in Belfast. It was a bitter blow: "I felt like Lucifer being thrown out of heaven." He taught for five years at Belfast Royal Academy.
In 1956 he did, however, complete a part time Master's thesis entitled The Transformation of Presbyterian Radicalism in the North of Ireland 1792-1825. When the Troubles began, foreign scholars queued to read it because it decisively addressed one of the great questions of Ulster history: why had the Ulster Presbyterian community, so inclined towards radicalism and republicanism in the 1790s, become so apparently conservative and unionist?
Stewart became a schoolteacher fellow at Peterhouse, Cambridge, in 1965 and published his first book, The Ulster Crisis, in 1968. The book doubled as his PhD and effectively won him a history lectureship at Queen's Belfast; his return to Northern Ireland coincided with the crisis generated by the civil rights movement there. In 1972 he published The Pagoda War; Lord Dufferin and the fall of the kingdom of Ava 1885-1886, which dealt with the British annexation of Burma.
The Narrow Ground confirmed his scholarly reputation, although not all the acclaim was welcome. The Reverend Ian Paisley held up the book up in front of his congregation and declared: "Here is a great book which tells us the truth about the history of Ulster." Stewart remarked with some anguish: "Obviously I, as an individual, have no control over what Dr Paisley does from the pulpit. I was astonished when I heard about it. I am not involved in any political party. I am not involved in politics."
Perhaps this political indigestion explains why Stewart found it so difficult to write his next book, a short and (by Stewart's standards) rather uninspired biography of Edward Carson, the great Unionist leader during the Ulster crisis of 1912-14.
Stewart was appointed a reader in 1975, but controversially was never granted a chair by Queen's Belfast. After taking early retirement in 1990, he embarked on a golden period of productivity. He returned to the theme of Ulster radicalism with two fine books: A Deeper Silence; the hidden origins of the United Irish movement (1993) and The Summer Soldiers; the 1798 rebellion in Antrim and Down (1998). He also edited Michael Collins; the secret files (1997) and produced a general survey, The Shape of Irish History.
Tony Stewart is survived by his wife, Anna, and two sons.
