Ethelbert was still a pagan, but his wife Bertha, daughter of King Charibert of the Franks, had been converted to Christianity. Sitting under a spreading oak, Ethelbert received the missionaries. After listening carefully to their words, he gave them permission to preach to his subjects. He also made over to them a house in Canterbury, with the use of the little stone church of St. Martin, which had stood there since the period of Roman occupation. This had formerly been the oratory of Queen Bertha and her confessor Liud hard. Ethelbert was converted and baptized at Pentecost, 597. After this promising start, Augustine went back to Provence to be consecrated bishop by Vergilius, metropolitan of Arles and papal legate for Gaul. On his return some ten thousand of Ethelbert's subjects were baptized in the Swale River.

Augustine, greatly heartened by the success of his mission, now sent two of his monks to Rome to report to the Pope, and to ask for more helpers. Also he wished to have the Pope's counsel on various problems. When the monks came back to England with a fresh band of missionaries, they brought the pallium for Augustine. Among the new group were Mellitus, Justus, and Paulinus, who was afterwards archbishop of York. With these "ministers of the Word," wrote the Venerable Bede, "the holy Pope sent all things needed in general for divine worship and the service of the Church, viz. sacred vessels, altar cloths, ornaments for churches, and vestments for priests and clerks, and also many books." The latter item was especially important, for the books helped to inspire the great love of learning which characterized the English Church.

Gregory sent to Augustine a plan for developing an ecclesiastical hierarchy and establishing a working organization for the whole country-a plan which was not fully carried out in Augustine's lifetime. There was to be a northern and a southern province, with twelve suffragan bishops in each. In a letter to Mellitus, which is presented earlier, following the life of St. Gregory, he gave instruction on other points, showing his administrative ability as well as considerable psychological insight. Pagan temples were, as far as possible, to be Christianized and retained. Consecration rites and feasts of martyrs were to replace the heathen festivals, for, Gregory wisely writes, "he who would climb to a lofty height must go by steps, not leaps."

In 603 Augustine rebuilt and reconsecrated the Canterbury church and the house given him by King Ethelbert. These structures formed the nucleus for his metropolitan cathedral. They were destroyed by fire in 1067, and the present cathedral, begun by the great Lanfranc in 1070, stands on their site. A converted temple outside the walls of Canterbury was made into another religious house, which Augustine dedicated to St. Peter and St. Paul. After his death this abbey became known as St. Augustine's.

With the King's support, the Christianization of Kent proceeded rapidly, but Gregory's charge had stated, "All the bishops of Britain we commend to your Fraternity." The survivors of the ancient British or Celtic Church and their bishops had been driven westward and southward into Wales and Cornwall by the Saxon conquerors of the fifth century. Here they had persisted as Christian communities, cut off from the outside world. Although they were sound in fundamental doctrine, some of their usages were at variance with those of Rome. Now, in virtue of his archiepiscopal jurisdiction, Augustine invited the Celtic bishops to meet with him at a spot outside the confines of Wessex, which has since come to be known as Augustine's Oak. In long conferences with the representatives of the Celtic Church Augustine urged them to comply with the customs of the rest of Western Christendom, in particular in the method of determining the date of Easter, and to aid him in converting the pagans. Loyalty to their own local traditions, however, and bitterness against their Saxon conquerors, made them unwilling to agree, even though Augustine performed a miracle of healing in their presence to prove the supernatural source of his authority. They consented to attend a second conference, held in Flintshire, but it too proved a failure. Augustine did not rise to greet his Celtic brothers when they arrived and they felt that he lacked Christian humility. They refused either to listen to him or acknowledge him as their archbishop. It was not until 664, at the Synod of Whitby, that their differences were resolved and ecclesiastical uniformity was established.

Augustine's last years were spent in spreading and consolidating the faith in Ethelbert's realm, which comprised large sections of eastern England south of Northumbria. Sees were established in London and Rochester, with Mellitus appointed bishop over one and Justus over the other. Seven years after his arrival Augustine died, leaving the continuation of his work to others.