He was a member of the O'Cleirigh Bardic family, and compiled with others the Annála Ríoghachta Éireann (Annals of the Kingdom of Ireland) at Bundrowse in County Leitrim on 10 August 1636.

As a member of one of the foremost learned families of Gaelic Ireland, Ó Cléirigh received a wide-ranging and thorough education.

He records that he was taught, for instance, by Baothgalach Mac Aodhagáin,[4] a learned cleric active in County Tipperary, who became the Bishop of Elphin.

[2] To do this, he returned to Ireland in 1626 and spent over a decade based at a Franciscan house by the River Drowes on the Donegal-Leitrim border.

[3] Ó Cléirigh travelled widely throughout Ireland during this period, collecting and transcribing a vast quantity of Irish texts.

[3] However, other important collaborators included Muiris mac Torna Uí Mhaolchonaire, and Ó Cléirigh's brother, Conaire.

[8] Among the other works copied and compiled in this period were: the medieval Irish account of clashes with the Vikings, Cogad Gáedel re Gallaib, twice, (in 1629, and again in 1636); the royal genealogy, Réim Ríoghraidhe[c] in 1630;[3] and Leabhar Gabhála (Book of Invasions) in 1631.

[10][11] The Mícheál Ó Cléirigh Institute for the Study of Irish History and Civilisation at University College Dublin is named in his honour.