The conversion of the English to Christianity began with the mission of Augustine of Canterbury, sent by Pope Gregory the Great to Kent in 597, and with the parallel work of Irish missionaries in the north. It was neither instant nor smooth: kingdoms lapsed back into paganism, and the process stretched across most of the seventh century before Christianity was securely established.
Our best narrative source, Bede's Ecclesiastical History, preserves telling moments, the counsel Gregory sent that pagan temples should be purified and reused rather than destroyed and that the people's festivals be redirected to Christian ends, and the famous scene at the court of Northumbria where a councillor likens human life to a sparrow's flight through a lighted hall. Some older customs persisted, folded into the Christian calendar or surviving as folklore, and the very names of the weekdays and of Easter carried the old gods' memory into the new faith, but organised Anglo-Saxon paganism as a living religion had effectively ended by around 700.