However, Bernard Bischoff and Michael Lapidge reconstructed his earlier life based on a study of texts produced by his Canterbury School.

[3] Theodore's childhood saw devastating wars between Byzantium and the Persian Sassanid Empire, which resulted in the capture of Antioch, Damascus, and Jerusalem in 613–614.

[11] The Synod of Whitby (664) having confirmed the decision in the Anglo-Saxon Church to follow Rome, in 667, when Theodore was aged 66, the see of Canterbury happened to fall vacant.

Following Wighard's death, Theodore was chosen by Vitalian upon the recommendation of Hadrian (later abbot of St. Peter's, Canterbury).

[12] Theodore conducted a survey of the English church, appointed various bishops to sees that had lain vacant for some time,[13][14] and then called the Synod of Hertford (673) to institute reforms concerning the proper calculation of Easter, episcopal authority, itinerant monks, the regular convening of subsequent synods, marriage and prohibitions of consanguinity, and other matters.

Theodore's intervention prevented the escalation of the war and resulted in peace between the two kingdoms,[12] with King Æthelred of Mercia paying weregild compensation for Aelfwine's death.

[16] Theodore and Hadrian established a school in Canterbury, providing instruction in both Greek and Latin, resulting in a "golden age" of Anglo-Saxon scholarship:[17] Theodore also taught sacred music,[17] introduced various texts, knowledge of Eastern saints, and may even have been responsible for the introduction of the Litany of the Saints, a major liturgical innovation, into the West.

[23] Theodore called other synods, in September 680 at Hatfield, Hertfordshire, confirming English orthodoxy in the Monothelite controversy,[24] and circa 684 at Twyford, near Alnwick in Northumbria.