The Assyrian Church of the East considers itself as the continuation of the Church of the East, a church that originally developed among the Assyrians during the first century AD in Assyria, Upper Mesopotamia and northwestern Persia, east of the Byzantine Empire. It is an apostolic church established by Thomas the Apostle, Addai of Edessa, and Bartholomew the Apostle.

The historical distinctiveness of the Assyrian Church of the East resulted from the series of complex processes and events that occurred within the Church of the East during the transitional period that started in the middle of the 16th century, and lasted until the beginning of the 19th century. That turbulent period was marked by several consequent splits and mergers, resulting in the creation of separate branches and rival patriarchal lines. During the entire period, one of the main questions of dispute was the union with the Catholic Church.