He was of noble birth, being a member of the MacCarthy Reagh family of Springhouse, Bansha, County Tipperary in Ireland who were Princes of Carbery and who subsequently became Counts of Toulouse in France.
On account of the Revolution, which broke out in France in May, 1789, and subsequently as the result of an accident whereby his spine was strained when he fell from a rickety stairs as he was carrying an immense bundle of firewood, to a frail old woman in an attic, his college career was interrupted.
In a short time he became famous as a preacher and theologian, and besides his eminent qualifications as an ecclesiastic, he was endowed with poetical talent, and composed Latin verse of a high order of merit.
In his deep humility, Abbe MacCarthy did not accept the episcopal office, and when close to fifty years old, he joined the Society of Jesus in 1818.
After a course of Lenten sermons at Annecy, Savoie, concluding on Easter Sunday, 7 April 1833, he was taken ill, and having expired in the Bishop's Palace in his 64th year, he was buried in the Cathedral there.