Baring-Gould’s sources: Named in many later Western Martyrologies, but not enrolled in the Roman Kalendar. He is variously called Adelhard, Adalarch, Alard, and Adelhardt. His life was written by S. Paschasius Radbertus, his disciple, and this was epitomized by S. Gerard, of Sauve-Majeur, in the 11th century. Paschasius says that the reason of his writing the life, was "to recall him whom almost the whole world regards as holy and admirable; whom we have seen, and whose love we enjoyed."

Adalhardt was of royal race, having been the son of Bernhardt, son of Charles Martel, the brother of King Pepin; so that Adalhardt was cousin-german to Charlemagne [king of the Franks, crowned emperor in 800], by whom he was called to court in his youth, and created Count of the Palace. But when the king put away his wife, the daughter of Desiderius, King of Italy, to marry another, Adalhardt left the court, disgusted with its lawlessness and vice, and became a monk at Corbie, at the age of twenty, in the year 773. He was made gardener, and, as his historian says, "With Mary he sought Jesus in the garden." At Corbie, he was so frequently visited by his relations, his friends, and acquaintances, that he had not sufficient solitude for the labour of turning his soul from earth to heaven; therefore he left Corbie and betook himself to Monte Cassino; but by order of the Emperor Charles, he was brought back again to Corbie, where he was shortly after elected abbot. He was compelled at last, by Charlemagne, to quit the monastery, and take upon him the charge of prime minister to his son Pepin, to whom he had intrusted the government of Italy.

On the death of Charlemagne, Louis the Pious succeeded to the throne, and dismissed all the old ministers and officers of his father. Bernard, son of Pepin, the elder brother of Louis, who was dead, having asserted his right to the throne, King Louis suspected the abbot of Corbie of having been privy to this attempt, and he exiled him to the island of Heri, or Herimoutier, and his brothers and sisters were sent into monasteries. His brother Walla was forced to become a monk at Corbie; Bernharius was sent to Lerins; his sister Gundrada was given to the charge of S. Radegund, at Poictiers, and only Theodradra was left unmolested at Soissons.

Adalhardt spent seven years in banishment at Herimoutier, and then the king, having recognized his error, recalled him, to the great grief of the monks of Heri, to whom his meekness and charity had made him dear, and to the joy of those of Corbie, to whom he returned. He was not, however, allowed to remain at peace in his abbey at the head of his monks, but was recalled to court, where the king, whose disposition was much changed, followed his advice in all his undertakings, and Adalhardt was of great use to him, in suggesting improvement in the laws. At length, in 823, he obtained leave to return to Corbie, which he governed till his death. He had an admirable memory, so that he never forgot the face, or name, or disposition of one of his monks; and he was careful to speak with each of them once a week.

During the banishment of the Saint, another Adalhardt, who governed the monastery by his appointment, began the foundation of another Corbie, in the diocese of Paderborn, in Westphalia, that it might be a nursery of missionaries for the conversion of the northern nations. S. Adalhardt often journeyed from one Corbie to the other, that he might provide for the welfare, and look to the discipline of both houses. Finding himself attacked with fever, and knowing that he should not recover, he used every effort to reach the mother house before Christmas. This he achieved, and there he calmly prepared for his passage, communicating daily. Hearing of his sickness, Hildemann, Bishop of Beauvais, who had been a monk under him, hurried to his side, and administered to him the Sacrament of extreme unction, and scarcely left him. One day, however, the bishop left the room for a moment, and, on his return, saw the sick man in great transport. The Abbot exclaimed, "Hither speedily, Bishop, I urge you, and kiss the feet of Jesus, my Lord, for He is at my side." Then the Bishop of Beauvais trembled with awe, and stood still, not knowing what to say or do. But Adalhardt said no more. On the Octave of the Nativity, he called together the brethren, and having received the Body and Blood of Christ, he said to the assembled monks, "O my sons, the fruit of my old age in the Lord! I have finished the number of my days, and to-day I shall depart, and go the way of all flesh, and appear in the presence of my Redeemer. I have finished the course of my struggle, and what reward I shall receive, I know not. But help me, I pray, that I in you, and you in me, may rejoice in the Lord." Thus saying, he surrendered his pure soul to Him who made it. He was buried at the foot of the chancel steps in the Church of S. Peter, at Corbie; but in the year 1040 the body was taken up and enshrined.