In AD890, at King Alfred's insistence, Plegmund was elected to the Archiepiscopate of Canterbury and was consecrated in Rome by Pope Formosas. The King styled him "Plegmund, my Archbishop," in the preface of a translation of Pope Gregory's Regula Pastoralis, a copy of which was sent to every Bishop throughout the kingdom. The copy presented by the King to Plegmund is still preserved in the British Library.

"Plegmund was chosen of God and of all the people Archbishop of Canterbury" in the year AD 890. In AD 908, he consecrated the New Minster which King Edward the Elder had founded at Winchester. During his pontificate, the West Saxon episcopate was subdivided with the creation of the Bishoprics of Wells and of Crediton. Many bishoprics had also become vacant due to Viking ravages and Plegmund threatened to excommunicate King Edward the Elder and place an interdict on the whole country if they were not filled as soon as possible. He got his way, and it is said that he consecrated seven Bishops in one day, in AD 909, of whom five were for Wessex. His death took place on 2nd August AD 923.