Born at Saul in 1571, Mac Aingil received his earliest education in his native place and then passed to a famous school in the Isle of Man. On his return to Ireland he was selected by Hugh, Prince of Tyrone, as tutor to his sons Henry and Hugh. He was sent by the prince as special messenger to the Court of Spain to solicit aid for the Ulster forces.
During his stay at Salamanca, where the Court then was, he frequented the schools of the university and took doctor's degrees in divinity. Soon afterwards he entered the Franciscan order where he enjoyed a great reputation as a theologian, and his commentaries on John Duns Scotus were held in high repute. It was principally due to his great influence at the Spanish Court that the Irish Franciscan College of St. Anthony was founded at Louvain.
After his entry into the order, Mac Aingil at first taught in the University of Salamanca, then he was appointed superior and lecturer at St. Anthony's, Louvain. He was summoned to Rome to lecture in the convent of Aracoeli. His energies were not limited to his work as professor; he was employed by the pope on several commissions. He gave substantial help to Father Luke Wadding in founding and developing St. Isidore's and the Ludovisi colleges for Irish students.
On 17 March, 1626, Urban VIII, passing over all the other candidates, nominated Mac Aingil as Archbishop of Armagh and Primate of all Ireland. He was consecrated, at the same time as Thomas Walsh, Archbishop of Cashel, on 7 June, in the church of St. Isidore.
MacAingil's health had been much weakened by his many duties and by the austerities he practised. In visiting the provinces of the order he always travelled on foot, and passed much time in prayer and fasting. While making preparation for his departure for his new duties in Ireland he caught fever and died. He was buried in the church of St. Isidore, and his friend Don John O'Neill, Earl of Tyrone, had a monument placed over his grave. Nicolaus Vernulæus delivered an oration before the university commemorating the virtues and learning of the archbishop, which was published at Cologne, 1657.
Mac Aingil's principal works are: Scoti Commentaria in quatuor libros Sententiarum, 2 vols., folio, Antwerp, 1620 (to this work is prefixed a life of Scotus); Scoti Commentaria seu Reportata Parisiensia; Quæstiones quodilibetales; Quæstiones in libros de anima; Quæstiones in metaphysicam; etc. He also wrote a work in Irish, which was printed at the Irish press in the college of St. Anthony's, Louvain, in 1618, entitled Scathain sacramunthe na Aithrighe, that is, "The Mirror of the Sacrament of Penance".