He succeeded his father  Eormenric in 560, as King of Kent and unsuccessfully tried to win from Ceawlin of Wessex the overlordship of Britain. His politics was advanced by his marriage with Bertha, daughter of Charibert, King of the Franks.  He gave her an old Roman church in his capital of Canterbury to practice her religion in, although he himself remained a worshipper of Odin. The same instinct of hospitality appears in his message to St. Augustine when, in 597, the Apostle of England landed.

After the arrival of the Roman missionaries his baptism in 597 had such an effect in deciding the minds of his wavering countrymen that as many as 10,000 are said to have followed his example within a few months. Thus Ethelbert became the father of the infant Anglo-Saxon Church. But, although he helped Augustine to convert a heathen temple into the church of St. Pancras, he never compelled his heathen subjects to accept baptism. Also as the lawgiver who with the ninety "Dooms of Ethelbert" issued the first written laws to the English people, he holds in English history a place which did more than any other for the upbuilding of free political institutions.