Armenian Orthodox catholicos (supreme head of the Armenian Church), a learned theologian and jurist who strove for greater ecclesiastical autonomy for the Armenian Church and supported the movement in the Eastern Church in favour of orthodox Christological theology.

With a reputation for learning, John was chosen catholicos in 718. Soon afterward he convened a national synod at Dvin to reform the Armenian Church's liturgy and its pastoral discipline. At first apparently in sympathy with the heterodox monophysites (q.v.) in the Eastern Church, he held a second national synod in 726 at Manzikert, near present Erzurum, Tur., to consider union with the Syrian Jacobite Church, a Monophysite community. John is noted for his attempt to reconcile the subtleties of Syrian and Armenian mystical Christology with the exactness of orthodox definitions. He thus sought to express his own theological tradition in terms consonant with the doctrinal decrees of the general council of Chalcedon (451).

John's principal writings include a theological treatise on Christ, in which he emphasized the reality of Christ's human nature and material body, in opposition to the view of the extreme Monophysites; a brief tract in which he argued for the preservation of the independent tradition of the Armenian Church within the Eastern Orthodox world; a discourse denouncing the Paulicians (a dualist Christian sect that emerged in the 7th century); and a reform of the structure and literary style of the Armenian psalter and prayer book.

Also credited to John is the Kanonagirk' (“Corpus of Canon Law”), the first collection of church legislation in the Armenian Church.

The writings of John of Odzun were edited in Armenian and translated into Latin by J.B. Aucher in 1838.