From his Georgetown faculty page, we learn that he is a prolific and award-winning author recognized as such all over the globe:
John O’Malley’s specialty is the religious culture of early modern Europe, especially Italy. He has received best-book prizes from the American Historical Association, the American Philosophical Society, the Sixteenth Century Studies Conference, and from the Alpha Sigma Nu franternity. His best known books are The First Jesuits (Harvard University Press, 1993), which has been translated into ten languages, and What Happened at Vatican II (Harvard, 2008). He has edited or co-edited a number of volumes....O'Malley is the author of several books, but will be in town in part to talk about his two most recent, both devoted to landmark councils of the Western Church, both of which have anniversaries this year: Trent: What Happened at the Council, which concluded 450 years ago this year; and of course What Happened at Vatican II, from 1962-65. Both of those councils had, of course, huge and dramatic consequences not only for the Catholic Church, but especially her relations with the Christian East. In the aftermath of Trent, and the creation of O'Malley's own Jesuit order, the Catholic Church rebounded in Eastern Europe and began, through a long, complicated process--best recounted in Boris Gudziak's splendid book, discussed here--what some Orthodox Christians see as improper incursions into what we today call Ukraine and Russia--and further East, also, creating problems for Orthodox Christians in places such as India and Ethiopia. If Trent seems--in the eyes of some--to have begun the dolorous process and period of "uniatism," creating such problems between East and West, particularly in areas under Hapsburg domination such as Galicia, then Vatican II undeniably and dramatically began to repair those relations and to allow East and West to begin the "dialogue of love" that has drawn both closer together.
John O’Malley has lectured widely in North America and Europe to both professional and general audiences. He has held a number of fellowships, from the Guggenheim Foundation, the National Endowment for the Humanities, the American Council of Learned Societies, and other academic organizations. He is past president of the Renaissance Society of America and of the American Catholic Historical Association. In 1995 he was elected to the American Academy of Arts and Sciences, in 1997 to the American Philosophical Society, and in 2001 to the Accademia di san Carlo, Ambrosian Library, Milan, Italy. He holds the Johannes Quasten Medal from The Catholic University of America for distinguished achievement in Religious Studies, and he holds a number of honorary degrees. In 2002 he received the lifetime achievement award from the Society for Italian Historical Studies and in 2005 the corresponding award from the Renaissance Society of America. He is a Roman Catholic priest and a member of the Society of Jesus.
Equally one can see a similar progression in Jesuit history and historiography, as O'Malley's celebrated confrere, Robert Taft, has noted: early Jesuits writing on and about Eastern Christianity tended to do so tendentiously with the prejudices of a high Tridentine triumphalism and aggressive apologetics (and often aggressive politics--which everyone in that period undertook: Lutheran, Anglican, Catholic, and Orthodox powers all over Europe); but later Jesuits, including those like Taft, O'Malley, Juan Mateos, Michael Fahey, Samir Khalil Samir, and others in our time (especially those associated with the Pontifical Oriental Institute) have been utterly invaluable in narrating objectively and fairly Eastern Christian history, Catholic-Orthodox history and relations, Orthodox-Muslim relations, and much else besides. Some might chafe at having Orthodox history told by Catholics, but show me where the comparable Orthodox scholars are. In point of fact, if it is genuine history and not what Taft calls "confessional propaganda," then the ecclesial affiliation of the historian should matter very little if at all. And that is what these Jesuits--and others--are especially good at: telling history without regard for whose ox gets gored, or whose cause promoted. (For this reason, someone like Robert Taft was given the rare distinction of double-pectoral insignia by no less a figure than the Ecumenical Patriarch himself, who recognized that Taft had done work of signal service to liturgiology and Orthodoxy more widely. Many Orthodox themselves, when Taft was still teaching in Rome, went to him to do their doctorates because they knew he was the world's specialist on Byzantine liturgical history.)
For this reason also, however, some have cast suspicions on O'Malley for not promoting robustly enough the currently favored interpretations about Vatican II (Trent seems sufficiently distant and obscure that nobody cares much about it anymore). Though it makes me nearly comatose whenever I hear this debate starting up again, Catholics have for years been banging on about a "hermeneutics of continuity" vs. a "hermeneutics of rupture" in understanding Vatican II. As I noted here, in discussing Congar's history of ecclesiology and his diaries of Vatican II, it seems to me highly problematic that apologists for Vatican II want to insist that everything done by the council and in its aftermath was good and in impeccable continuity with previous practice and teaching, and no suspicion about the council can ever be raised. What a lot of nonsense that is. Though one needn't subscribe to the views of such as the Society of St. Pius X (SSPX), a group I find risible and repellent on most matters, one can nonetheless sympathize with their difficulty in reconciling what the council taught with what previous popes, for example, taught on certain questions not least because earlier papal (and even conciliar) teaching and practice was, in some instances, explicitly abandoned at Vatican II or otherwise greatly changed.
One can, moreover, join with them in recognizing that not everything to come out of Vatican II succeeded. This is not and need not be a "controversial" position but an entirely human recognition of the vicissitudes of history and the complexities of any human gathering. Anybody who knows anything about any council of the Church--local, regional, or ecumenical; Eastern or Western--knows that some councils succeed, some fail (e.g., Ferrara-Florence), and most only succeed partially (Nicaea I was partially successful in dealing with Arianism, but Constantinople I was also required to deal with the heresy). Even the current pope has admitted that not all councils are successful, and that parts of Vatican II could not be counted an unmitigated success. Why can we not be honest about this? Why do apologists continue with their ham-fisted insistence that Vatican II really changed nothing that went before when it's manifestly obvious that it did? While major dogma (a category many people are likely unable to differentiate sufficiently from lesser matters, thus leading to the impression on the part of some Catholics that Vatican II basically created an entirely new Church--new Mass, new married diaconate, new liturgical rites and languages, etc.) may have been untouched, many other important matters did in fact change, and for the better--the Catholic Church's relationship with Israel, Islam, and the Christian East being the three greatest of those highly welcome changes, alongside new understandings of human rights, including religious freedom and Church-state relations.
Part of the answer to this question about why we cannot honestly admit to certain changes lies, I think, in what John Allen discusses so insightfully in his book All the Pope's Men: The Inside Story of How the Vatican Really Thinks. There Allen notes how much of Vatican thinking is governed by Italian cultural codes in which la bella figura must be maintained at all times in the face of any change, good or bad. The important thing is to look lovely and undisturbed. One mustn't startle the horses. (As the fictional Prime Minister Jim Hacker puts it in the hilarious British comedy Yes, Prime Minister, when he's asked to appoint a bishop in the Church of England, the Church "mustn't look political" even when it is.)
O'Malley has himself told the history of the popes in another recent book, which I reviewed elsewhere: A History of the Popes: From Peter to the Present. This is a very solid, reliable, even-handed telling of the history of the longest continual office of governance in the Western world and its colorful incumbents. It is difficult to compress 2000 years of history into one book, but O'Malley has managed that in a way that is both erudite and accessible. About this book the publisher tells us:
A History of the Popes tells the story of the oldest living institution in the Western world—the papacy. From its origins in Saint Peter, Jesus' chief disciple, through Pope Benedict XVI today, the popes have been key players in virtually all of the great dramas of the western world in the last two thousand years. Acclaimed church historian John W. O'Malley's engaging narrative examines the 265 individuals who have claimed to be Peter's successors. Rather than describe each pope one by one, the book focuses on the popes that shaped pivotal moments in both church and world history. The author does not shy away from controversies in the church, and includes legends like Pope Joan and a comprehensive list of popes and antipopes to help readers get a full picture of the papacy. This simultaneously reverent yet critical book will appeal to readers interested in both religion and history as it chronicles the saints and sinners who have led the Roman Catholic Church over the past 2000 years.