Esposito, Mario (1887–1975), medievalist and Hiberno-Latinist, was born 7 September 1887 in Blackrock, Co. Dublin, third child and only son of Michele Esposito (qv), professor of music in the Royal Irish Academy of Music, and Natalia Esposito (née Klebnikoff). His father occupied for many years the centre of the Dublin musical scene. Nothing is known of Mario's youth. It would seem that he received his early education at home from his highly educated and multilingual parents. He entered TCD (1905) at the age of 18, and was awarded his BA in 1912. He was elected a member of the RIA in 1910, but his membership lapsed in 1926. Although encouraged by his parents to take up chemistry, he very quickly became an avid student of medieval manuscripts and of the Latin literature written by Irishmen at home and abroad during the middle ages. He may be credited with having coined the term ‘Hiberno-Latin’. During visits to Britain (1907–8) he visited several archives and libraries, and apparently made the acquaintance of the great English medievalist M. R. James. In 1909 and 1912 he visited the libraries of Switzerland and Belgium. He studied medieval Latin palaeography and poetry under Wilhelm Meyer in Göttingen (1913–14). His knowledge of medieval manuscripts and of incunabula had few rivals, as his copious articles on Hiberno-Latin and medieval literature generally at that time, and for many years afterwards, show.
He and his family took some part in assisting Sinn Féin and the IRA during the years of the struggle for Irish independence. He acted as courier for Éamon de Valera (qv), then president of Sinn Féin, to other rebels in London and Manchester. In 1919 he was sent by Michael Collins (qv), with another, to represent Sinn Féin's demand for independence at the peace talks in Versailles, but apparently got no further than the libraries of Switzerland, and failed to report back to Dublin. He went back to London in the middle of 1919, perhaps out of fear of retribution by either Sinn Féin or the British forces in Ireland. In the following year he returned to his mother and sister Vera in Florence, Italy, where his father had a small villa and where he remained for the rest of his life. He was, by all accounts, reclusive and ascetic (a vegetarian and a lifelong celibate and non-drinker), who kept the details of his private life a close secret. However, he maintained an extensive learned correspondence with many scholars in Ireland and on the Continent, and with libraries throughout Europe. It is thought that he played some part in resisting the Nazis in Italy (1943–5) but, like his work for the IRA, this was done in a very covert way which has left no paper trail. Thus, those who knew him as a scholar knew nothing of his IRA activities, and vice versa. He never sought or gained any chair or other academic post, and maintained himself frugally through the money from his father's estate and the rent which the family – two elderly, eccentric sisters and a brother – obtained from letting out the lower floor of the house. In latter years, having survived his two sisters, he sold off his collection of incunabula piecemeal. He died on 19 February 1975. On his instructions, his papers and personal effects were destroyed after his death by a family friend and minder. Most of the copies of his privately published autobiography, Montagne, amore e libertá: Saggi e ricordi di Mario Esposito (1944), were destroyed by the Nazis, and no copy can now be traced.
Esposito was a pioneer in the field of Hiberno-Latin, along with Ludwig Bieler (qv) and other foreign scholars. In a massive outpouring of notes, papers, and books published between 1905 and 1961 he laid the foundations for the critical study of the subject and unearthed much of the vast and scattered manuscript resources for it. His publications show that he maintained an interest in medieval heretical texts and movements and related studies. He could be a severe critic of the proponents of a ‘golden age’ of Irish learning, and sometimes made hasty and superficial judgments on the subject. But his earnestness, sincerity, and prodigious industry as a scholar cannot be doubted.