[1] He was born at Erinagh House, Castleconnell, County Limerick, the son of Admiral Hayes O'Grady.
He was a cousin of the writer Standish James O'Grady, with whom he is sometimes confused.
Although qualified as a civil engineer, he is best remembered for Silva Gadelica (two volumes, 1892), a collection of tales from medieval Irish manuscripts.
In 1901 he contributed an essay on Anglo-Irish Aristocracy to a collection entitled Ideals in Ireland edited by Augusta, Lady Gregory.
His Catalogue of the Irish Manuscripts in the British Museum was unfinished on his death and was completed by Robin Flower.