Boniface was a Roman, the son of a priest named Jocundus, and by tradition he had himself been married before his wife's death and his entry into the higher service of the Church. He is believed to have received ordination from the hands of Pope Saint Damasus I, and around the year 405 he was sent as the representative of Pope Innocent I to Constantinople, a mission that made him familiar with the wider Church and with the delicate business of dealing with emperors. Under Innocent he served as a trusted counsellor, and he held the title of the church of San Lorenzo in Damaso. Butler records that he was a priest "of an unblemished character, well versed in the discipline of the church, and advanced in years" when the burden of the papacy fell upon him.
Pope Zosimus died in December 418, and Rome fell into one of the sorrowful double elections that troubled the early Church. Immediately after the funeral at Saint Lawrence outside the Walls on 27 December, a faction of the clergy, chiefly deacons, seized the Lateran basilica and, driving back the senior clergy who tried to enter, elected the archdeacon Eulalius. The following day the majority of the Roman priests gathered in the church of Santa Teodora and elected the aged Boniface — expressly, as the report later sent to the emperor testified, against his own will. On Sunday, 29 December, both men were consecrated: Eulalius in the Lateran, Boniface in the church of Saint Marcellus in the Campus Martius, supported by nine metropolitans, some seventy priests, and the greater part of the people.
The city was thrown into confusion. The urban prefect Aurelius Anicius Symmachus, unfriendly to Boniface, reported to the Emperor Honorius at Ravenna that Eulalius, having been chosen first and in due order, was in the right, and on 3 January 419 the emperor confirmed Eulalius. Violence broke out between the two parties; Boniface was seized by the prefect's police and detained in a lodging outside the walls. Yet he bore the humiliation without breaking the peace. His supporters petitioned the emperor, alleging irregularities, and Honorius suspended his earlier decision, summoned both parties before himself and certain Italian bishops on 8 February, and then deferred the matter to a larger council, commanding both claimants to remain outside Rome. Boniface withdrew obediently to the cemetery of Saint Felicitas on the Via Salaria; Eulalius was sent to Antium, and the bishop Achilleus of Spoleto was appointed to celebrate the Easter rites in the vacant city.
Boniface obeyed; Eulalius did not. Impatient, he re-entered Rome on 18 March, rallied his followers, and on Holy Saturday, 29 March, occupied the Lateran, determined to celebrate Easter there in defiance of the imperial command. Troops were ordered to remove him so that Achilleus might officiate. Deeply offended, Honorius refused to hear Eulalius further and on 3 April 419 recognized Boniface as the lawful pope. On 10 April Boniface returned to Rome amid the acclamations of the people. Eulalius, who died in 423, was afterwards given a bishopric outside the city; the schism had lasted some fifteen weeks. Early in 420 an illness of the pope stirred his rivals' hopes again, and when he recovered Boniface, thinking not of himself but of the Church's future peace, asked the emperor on 1 July 420 for a law against renewed schism: Honorius decreed that where two claimants were contested, neither should be bishop, but only one chosen afresh by unanimous consent.
His pontificate, though short, restored the dignity of the Apostolic See. He was, in Butler's words, a lover of peace and remarkable for his mildness, yet he was not soft where the rights of souls and of the Church were at stake. He ordered the singing of the Gloria in excelsis on Maundy Thursday and regulated many points of ecclesiastical discipline. In Gaul he reversed his predecessor's concentration of power, reducing the sweeping vicariate authority of Patroclus of Arles and restoring the metropolitan rights of Narbonne and Vienne and of the chief bishops of the provinces; in 422 he upheld Hilary, archbishop of Narbonne, in his choice of a bishop for the vacant see of Lodève against Patroclus's candidate. He insisted that Maximus, bishop of Valence, be tried for his alleged crimes not by a single primate but by a synod of the Gallic bishops, promising to abide by their judgment — a shepherd more concerned with justice than with the exercise of his own power. When Antony of Fussala appealed to him in 422, he ruled that the man should be restored only if his innocence were proved.
In the East he watched jealously over the ancient rights of the Roman See in Illyricum, which the patriarch of Constantinople sought to absorb. He sustained his vicar Rufus, bishop of Thessalonica, allowing no episcopal election in Thessaly and Greece to stand without his confirmation, and in 421 declined to ratify the election of Perigenes as bishop of Corinth unless Rufus recognized him. Through his complaints to Honorius he persuaded the Eastern emperor Theodosius II to restore Illyricum to the jurisdiction of Rome. Writing to the bishops of Thessaly in 422, he was the first to use the word principatus of the Roman Church, and in his third letter to Rufus he declared that the blessed apostle Peter had received from our Lord's own sentence and commission the care of the whole Church.
Against the Pelagians, who denied the necessity of grace, Boniface showed unwearied zeal. Receiving two Pelagian letters that slandered Saint Augustine, he sent them straight to the bishop of Hippo, and Augustine, in gratitude for such solicitude, dedicated to him his reply, the four books Against Two Letters of the Pelagians. Boniface also obtained imperial support in requiring all bishops to subscribe to the Tractoria of Pope Zosimus condemning the heresy. Thus the humble old priest who had been dragged unwilling to the Chair of Peter became the friend and shield of the Church's greatest doctor.
Boniface died in Rome on 4 September 422 and was buried near the tomb of Saint Felicitas on the Via Salaria, in the cemetery where he had once waited in exile. The Church honors him as a saint; his feast is kept on 4 September, and in the older Roman calendar and in Butler's Lives on 25 October. His life teaches that authority is safest in the hands of a man who never sought it, and that meekness under injury and firmness in defense of the truth are not opposites but the two hands of one charity.
May Saint Boniface I obtain for us the grace to accept whatever burden God lays upon us without ambition and without resentment, and to defend the truth today with the same peaceable courage that marked his short and faithful reign.