Grandson of Tuathal Ó Cléirigh, a chief of the sept of Uí Chléirigh in Donegal, he was born in Kilbarron near Creevy, between Rossnowlagh and Ballyshannon on Donegal Bay.
As a member of one of the foremost learned families of Gaelic Ireland, Ó Cléirigh received a wide-ranging and thorough education.