first bishop of Rochester and fourth archbishop of Canterbury, under whose archiepiscopacy Northumbria was converted to Christianity.

In 601 he was sent by Pope St. Gregory I the Great to assist Archbishop St. Augustine of Canterbury in the conversion of England to Christianity. He was consecrated by Augustine as bishop of Rochester when the see was established in 604. Soon the Christian king Aethelberht of Kent built his cathedral, St. Andrew's, at Rochester, and granted Justus lands nearby. An anti-Christian reaction followed Aethelberht's death (616), and Justus fled to Gaul. He returned in 617, when Aethelberht's successor, Eadbald, recalled him to his bishopric. He became archbishop of Canterbury in 624 on the death of St. Mellitus. There followed the conversion of Northumbria by St. Paulinus, whom Justus consecrated as the first bishop of York. Justus' feast day is kept in the diocese of Southwark, London.