Charles O’Conor, Irish priest and historical author, is born at Bellanagare, County Roscommon, on March 15, 1764. He is chaplain and librarian to the Marchioness of Buckingham and catalogues many manuscripts, including the famous Stowe Missal, now in the Royal Irish Academy (RIA) in Dublin.

O’Conor is the second of six sons of Denis O’Conor and Catharine O’Conor (neé Browne), who also have six daughters. The O’Conors are Catholic, descendants of a princely family in the west of Ireland. His grandfather is the historian Charles O’Conor, his brother the historian Matthew O’Conor.

O’Conor is educated at the Pontifical Irish College, Rome, from 1779 to 1791 and is appointed parish priest of Kilkeevan, County Roscommon, in 1789. In 1796 he prepares for publication a memoir of his grandfather, the historian Charles O’Connor, which highlights the efforts made by him and other Irish Catholics of substance to obtain the constitutional repeal of the penal laws. The first volume is suppressed as dangerous to the family and the manuscript of the second is burned by O’Conor before reaching the printer. He destroys what he believes to be the whole run of the first volume and ten folios of the second, by casting them into a sewer, which communicates with the River Poddle. However, copies of the first volume survive in Trinity College Dublin (TCD) and the Barrister at Law (BL).

In 1798 O’Conor is invited to become chaplain to Mary Nugent, the Marchioness of Buckingham, and to organize and translate a collection of Gaelic manuscripts at Stowe, Buckinghamshire, England. With him he brings papers of his grandfather to Stowe, including fifty-nine Gaelic manuscripts. There he writes Columbanus ad Hibernos (1810–13), a series of letters supporting the royal veto on Catholic episcopal appointments in Ireland. These are answered by Francis Plowden and see him suspended from duties of parish priest by John Troy, Archbishop of Dublin. In his duties as librarian, he edits the Annals of the Four Masters, and other chronicles from the Stowe Library as Rerum Hibernicarum Scriptores Veteres (1814–26), an edition regarded as unreliable.

O’Conor experiences mental illness and by 1827 is suffering from the delusion that he is deliberately being starved by order of the Marquess of Buckingham. He leaves Stowe on July 4, 1827. The Nation (March 26, 1853) claims that he is thereafter a patient at Dr. Harty’s asylum in Finglas, Dublin, apparently along with John Lanigan, whom he knew in the Irish College. His family twice unavailingly demands that the paper’s editor issue a correction.

O’Conor dies on July 29, 1828, in his family’s house at Bellanagare. He is buried in Ballintober Cemetery, Castlerea, County Roscommon.