MacDonagh, Oliver Ormond Gerard (1924–2002), historian, was born 23 August 1924 in Carlow town, elder son of Michael MacDonagh (1892–1972), bank official from Limerick, and his wife Loretto Oliver (1897–1970). His childhood was spent in Roscommon town, where his father was posted, and he was educated there by the Christian Brothers, completing his secondary schooling at Clongowes Wood College, Co. Kildare. He was devoutly Roman Catholic; an exemplar was John Henry Newman (qv), who MacDonagh revered as a catholic, a thinker, and a writer, and about whom he wrote.
Studying under R. D. Edwards (qv), MacDonagh graduated with first place in the BA at UCD in 1944. Following distinctions in King's Inns examinations, he was called to the bar in the following year, but never practised. Sport remained a passion: he supplemented his student allowance as an occasional racing tipster for the Irish Times, enjoyed playing tennis, and took a particular interest in rugby, especially the fiery Munster variety. His UCD MA thesis on Irish emigration (1946) formed the basis of a seminal contribution on the subject in The great famine (1956). He went up to Peterhouse, Cambridge, in 1947 on an NUI travelling studentship. His first major work, derived from his Cambridge Ph.D. (1950), was ‘The nineteenth century revolution in government’ in the Historical Journal (1959), followed by a book, A pattern of government growth 1800–1860: the passenger acts and their enforcement (1961). The model of the nineteenth-century state's expansion outlined in these writings was as significant in stimulating research and debate as was that of MacDonagh's contemporary, Geoffrey Elton, in the area of Tudor government. Taking account of the work sparked by his thesis, he refined his own ideas further in Early Victorian government 1830–1870 (1977). MacDonagh himself felt that his best work was The inspector general: Sir Jeremiah Fitzpatrick and social reform 1783–1802, mainly because of the research challenge involved.
He was elected a fellow of St Catharine's College, Cambridge (1950; visiting fellow 1985, honorary life fellow 1987), and appointed college lecturer in history (also 1950), director of studies in history (1951), college librarian (1952), and university assistant lecturer (1959). MacDonagh went in 1963 as visiting fellow to the Australian National University (ANU), becoming (1964) foundation professor of history at Flinders University, New South Wales, where he blossomed as an administrator, but at the expense of research and writing. This was also his fate when, largely for family reasons, he came to UCC as professor of modern history and chairman of the joint history board (1968).
A visiting professor at Yale (1970–71), in 1973 he returned to Australia, to a post occupied till his retirement in 1989, as W. F. Hancock professor of history in the ANU's Institute of Advanced Studies in Canberra. Freed from administrative duties, this period was his most productive. Describing himself as ‘a last general practitioner among consultants’ (obit, Ir. Times, 8 June 2002) his interests lay largely in three fields: Ireland, Australia, and literary history. Australia lent perspective to his writings on Irish history and his earlier Ireland (1968) was reissued, revised and expanded, in 1983. Ireland: the union and its aftermath was published in 1977. States of mind: a study of Anglo-Irish conflict (1983), a series of essays which broke new ground in the interpretation of nineteenth-century Irish history, was awarded the Ewart-Biggs memorial prize in 1985. MacDonagh's finest work was probably his two-volume biography of Daniel O'Connell (The hereditary bondsman: Daniel O'Connell 1775–1829 (1988) and The emancipist: Daniel O'Connell 1829–1847 (1989)). It emphasised O'Connell as the modernising progenitor of catholic liberalism and of mass democratic politics in Ireland, and his importance in the European context, all expressed with a delicate erudition. He contributed the introduction and four chapters on Ireland 1830–45 to A new history of Ireland, v (1989). A history of Guinness, commissioned from him (and S. R. Dennison) in his Cambridge days, finally appeared (Guinness 1886–1939) in 1998, its publication having been vetoed for many years by the company. His other writings on Ireland covered topics as varied as culture and nationalism, banking history, nineteenth-century sea communications, eighteenth-century colonial nationalism, and even modern politics (Crane Bag (1985)). MacDonagh was an editor of the prestigious series Studies in Irish History which published original monographs in the 1970s.
His considerable administrative talents were seen to best effect in his central role as one of the instigators and chief manager of the multi-contributor eleven-volume history, Australians: an historical library (1988), produced – on time and within budget – for the Australian bicentenary. In its Guide and index (1988) MacDonagh contributed a typically valuable piece on the making of the history itself. Conscious of the organic intertwining of the two nations, he wrote extensively on Ireland and Australia, culminating in The sharing of the green: a modern Irish history for Australians (1996), completed while foundation professor at the Australian Catholic University (1994–6).
A gifted teacher, MacDonagh used enthusiasm and challenge to bring out the best in his pupils. He set great store by clarity of expression as a tool to test the logic of the historian's hypotheses, evidenced by the sophisticated and elegant writing style which distinguished him from many of his contemporaries.
His interest in literary history was first indicated in his pamphlet The nineteenth century novel and Irish social history (1970). Among his many works on Jane Austen, his critique Jane Austen: real and imagined worlds (1991) was well received. MacDonagh claimed that her books had initially inspired his interests in early nineteenth-century society and government. A work on Trollope was planned but never completed because of his declining health, particularly his eyesight. A mellifluous and resonant bass-baritone, he was a much-sought-after public speaker and was a frequent broadcaster in Australia. A bibliography to 1989 is in F. B. Smith (ed.) Ireland, England and Australia: essays in honour of Oliver MacDonagh (1990). Awarded an honorary D.Litt. by Flinders University (1983) and the NUI (1989), he was elected a member of the RIA (1993) and, variously, a fellow of the Australian Academy of the Social Sciences (1965; executive director 1991–2), the Australian Academy of the Humanities (1975) and the British Academy (1985). He died in Sydney, Australia, on 22 May 2002 and is buried at Macquarie Park cemetery, Sydney.
He married (1952) Carmel (b. 1928), elder daughter of Daniel J. Hamilton. They had three sons and four daughters.