He was baptized Maelmhaedhoc (a name which has been Latinized as Malachy) and was trained under Imhar O’Hagan, subsequently Abbot of Armagh. After a long course of studies he was ordained priest by St. Cellach (Celsus) in 1119. In order to perfect himself in sacred liturgy and theology, he proceeded to Lismore, where he spent nearly two years under St. Malchus. He was then chosen Abbot of Bangor, in 1123. A year later, he was consecrated Bishop of Connor, and, in 1132, he was promoted to the primacy of Armagh.
St. Bernard gives us many interesting anecdotes regarding St. Malachy, and highly praises his zeal for religion both in Connor and Armagh. In 1127 he paid a second visit to Lismore and acted for a time as confessor to Cormac MacCarthy, Prince of Desmond. While Bishop of Connor, he continued to reside at Bangor, and when some of the native princes sacked Connor, he brought the Bangor monks to Iveragh, County Kerry, where they were welcomed by King Cormac. On the death of St. Celsus (who was buried at Lismore in 1129), St. Malachy was appointed Archbishop of Armagh, 1132, which dignity he accepted with great reluctance. Owing to intrigues, he was unable to take possession of his see for two years; even then he had to purchase the Bachal Isu (Staff of Jesus) from Niall, the usurping lay-primate.
During three years at Armagh, as St. Bernard writes, St. Malachy restored the discipline of the Church, grown lax during the intruded rule of a series of lay-abbots, and had the Roman Liturgy adopted.
St. Bernard continues: Having extirpated barbarism and re-established Christian morals, seeing all things tranquil he began to think of his own peace. He therefore resigned Armagh, in 1138, and returned to Connor, dividing the see into Down and Connor, retaining the former. He founded a priory of Austin Canons at Downpatrick, and was unceasing in his episcopal labours.
Early in 1139 he journeyed to Rome, via Scotland, England, and France, visiting St. Bernard at Clairvaux. He petitioned Pope Innocent for palliums for the Sees of Armagh and Cashel, and was appointed legate for Ireland. On his return visit to Clairvaux he obtained five monks for a foundation in Ireland, under Christian, an Irishman, as superior: thus arose the great Abbey of Mellifont in 1142. St. Malachy set out on a second journey to Rome in 1148, but on arriving at Clairvaux he fell sick, and died in the arms of St. Bernard, on 2 November.
Numerous miracles are recorded of him, and he was also endowed with the gift of prophecy. St. Malachy was canonized by Pope Clement (III), on 6 July, 1199, and his feast is celebrated on 3 November, in order not to clash with the Feast of All Souls.
An account of the relics of St. Malachy will be found in Migne, Patrologiae cursus completus, CLXXXV.
From the Catholic Encyclopedia