Jaenbert was a native Kentishman was became the Abbot of St. Augustine's, Canterbury. At the death of Archbishop Bregowine, a contest took place between the monks of St. Augustine's and the monks of Christ Church (Canterbury Cathedral) with regard to his place of burial. Eventually the monks of Christ Church retained the body, but they elected Jaenbert to the Archbishopric, on 2nd February AD 765, at a church council at which King Offa of Mercia was apparently present. The following year, he was consecrated, in Rome, by Pope Paul I.
It may be that Jaenbert encouraged the people of Kent to rebel against Mercian domination, which they did at the Battle of Otford in AD 776. He certainly quarrelled with King Offa and began to spread rumours that the monarch was plotting with the Emperor Charlemagne to have the Pope deposed. In retaliation, Offa formed a scheme for abolishing the primatial dignity of Canterbury by converting Lichfield into a Metropolitan See. He obtained the consent of Pope Hadrian II and, at the Synod of Chelsea in AD 787, Jaenbert was compelled to relinquish several Dioceses which belonged to the Province of Canterbury. Jaenbert held a number of other synods at Brentford and Aclea, as well as Chelsea; but he shunned Clofesho (possibly Brixworth in Northamptonshire) because of its strong connections with the Mercian monarchy. One of his major objectives seems to have been the recovery of the monastery at Cookham (Berkshire) from Royal control.
He died on 12th August AD 792 and was buried in his old Monastery, St. Augustine's. His Feast Day is August 12th.
Edited from G.M. Bevan's "Portraits of the Archbishops of Canterbury" (1908).