Twice offered the Archbishopric of Canterbury, England; he declined, citing unworthiness. When Saint Theodore of Tarsus was sent instead, Adrian went as his assistant with special support to aid the monastic movement in the region. Detained in France due to suspicions of espionage for the emperor. Arrived in England in 669. Abbot of Saint Peter‘s, a monastery founded by Augustine of Canterbury.
Adrian and Theodore were highly successful missionaries in largely pagan England. In addition, Adrian was a great teacher of languages, mathematics, poetry, astronomy, and Bible study. Under his leadership, the School of Canterbury became the center of English learning. Worked to unify the customs of the English with the Church, and to promote Roman customs.