Maverick medieval historian and fellow of Trinity College Dublin

James Francis Lydon, who has died aged 85, was an outstanding Irish medieval historian.

He openly asserted that he was a nationalist historian, to whom the Irish language was of the greatest importance, and who, according to his colleague Prof Seán Duffy of Trinity College Dublin, remained all his life "a very devout Catholic who wore his faith on his sleeve".

On the other hand, Lydon believed strongly in the separation of church and State, and hugely admired the Presbyterian contribution to Irish Republicanism.

He adored Trinity College, his academic home for 33 years, where he was Lecky Professor of (Medieval) History for 13 years from 1980, and of which he was a fellow.

He also played a significant role, with David Thornley, in the 1960s in challenging Archbishop John Charles McQuaid's ban on Catholics from attending Trinity.

Disagreed
Lydon disagreed with his colleague TW Moody, Erasmus Smith Professor of (Modern) History at Trinity, often regarded as one of the father figures of so-called revisionist history in Ireland, that history was not a matter of opinion.

He told Duffy in an interview, published in History Ireland magazine in 1995, that "history is always a matter of opinion [and] for that reason is of its nature revisionist".

Therefore, in what was arguably the best tradition of historians, he refused categorisation or stereotyping.

Born in 1928 in Galway into a large family originally from Connemara, the young James grew up spending a great deal of time with his mother’s native-speaking family, becoming a fluent Irish speaker.

He was educated at University College Galway, now NUI Galway, graduating in 1950 with a double first in English and history. One of his external examiners was JRR Tolkien, author of The Lord of the Rings, who was so impressed with Lydon that he took him out to tea, having been refused permission by the university to take the young student to lunch!

Doctorate
Lydon went on to take his doctorate at London University under the great medievalist Sir Maurice Powicke, and returned to lecture at University College Galway in 1957, after a lengthy period travelling Europe.

His doctoral thesis was a study of the Irish contribution to the financing of the English king’s wars against Scotland in the late 13th and early 14th centuries, a subject which led him to a life-long study of the English political administration of Ireland in the later Middle Ages.

This would crystallise later in his classic work The Lordship of Ireland in the Middle Ages (1972), which he regarded as his major contribution to historiography.

Unorthodox
The book was typically unorthodox. An enjoyable read, without footnotes, The Lordship was an expression of Lydon's firmly held view of the necessity of engaging the student by conveying his own enthusiasm for his subject.

A participant in University College Galway’s drama society as an undergraduate, Lydon told Duffy if “you want to be a good lecturer, you have to be an actor”.

His later general survey of Irish history, a contemporary complement to Edmund Curtis's A History of Ireland – which he greatly admired – had a bias towards medieval and early modern Ireland.

This may have been due to a certain coolness towards more recent Irish “patriots”. He admired Michael Collins “marginally”, as he told Duffy in the 1995 interview, but, pointedly, “not Éamon de Valera”.

Deeply passionate about music, especially opera, Lydon battled depression in later years. Like several of his siblings, he remained unmarried. He is survived by a nephew and sister-in-law.