He was chaplain and librarian to the Marchioness of Buckingham and catalogued many manuscripts, including the famous Stowe Missal, now in the Royal Irish Academy.
Charles O'Conor was educated in Ludovisi College, Rome from 1779 to 1791 and was appointed parish priest of Kilkeevin, County Roscommon (1792–98).
[2] In 1798 he was invited to become chaplain to Mary Nugent, the Marchioness of Buckingham and to organize and translate a collection of Gaelic manuscripts at Stowe.
In Stowe O'Conor wrote Columbanus ad Hibernos (1810–13),a series of letters supporting the royal veto on Catholic episcopal appointments in Ireland.
These were answered by Francis Plowden and saw him suspended from duties of parish priest by John Troy, Archbishop of Dublin.