He overthrew the previous ruler, Ceolwulf, in 823. He claimed authority over the Welsh Kingdom of Powys later in the same year, after decades of warfare between it and the Mercians. Despite this early success, however, Beornwulf's reign was a short one: he became engaged in a dispute with Egbert of Wessex over control of Kent, and this led to a battle between them at Ellandun. Beornwulf was defeated, and the West Saxons triumphantly marched on into Kent, deposing its pro-Mercian ruler, Baldred.