Justus was the first bishop of Rochester and fourth archbishop of Canterbury. He died at Canterbury November 10, 627.

He was sent to England with Mellitus and others in 601. Augustine consecrated him bishop for West Kent in 604 and King Ethelbert of Kent built him a church at Rochester.

In 617 during the heathen reaction under Eadbald, with Mellitus he fled into Gaul, but was recalled after a year and restored to his bishopric (see Laurence of Canterbury).

He succeeded Mellitus as archbishop in 624, consecrated Romanus as his successor at Rochester, and sent Paulinus to Northumbria. He received the pallium from Pope Boniface V.