As archbishop, he had a difficult relationship with King Offa of Mercia, who at one point confiscated lands from the archbishopric.
By 787, some of the bishoprics under Canterbury's supervision were transferred to the control of the newly created Archbishopric of Lichfield, although it is not clear if Jænberht ever recognised its legitimacy.
Jænberht was a monk at St Augustine's Abbey, Canterbury before being selected as abbot of that monastic house.
[6] During Jænberht's term of office, a dispute arose between the see of Canterbury and Offa which led in 787 to the creation of the rival Archdiocese of Lichfield under Hygberht.
[10] Matthew Paris, writing in the thirteenth century, stated that Jænberht conspired to admit Charlemagne to Canterbury if he invaded Britain.
[12] Jænberht presided at a council held at London, sometime after the elevation of Lichfield, attended by most of the bishops from southern Britain.