He was born in Constantinople as the son of Theodore and Eudokia, of a strictly orthodox family, which had suffered from the earlier Iconoclasm. His father Theodore, one of the secretaries of Emperor Constantine V Kopronymos, had been scourged and banished to Nicaea for his zealous support of Iconodules, and the son inherited the religious convictions of the father. Nevertheless he entered the service of the Empire, became cabinet secretary, and under Irene took part in the synod of 787 as imperial commissioner. He then withdrew to one of the cloisters that he had founded on the Propontis, until he was appointed director of the largest home for the destitute in Constantinople in c. 802.
After the death of the Patriarch Tarasios, although still a layman, he was chosen patriarch by the wish of the emperor (Easter, April 12, 806). The uncanonical choice met with opposition from the strictly clerical party of the Stoudites, and this opposition intensified into an open break when Nikephoros, in other respects a very rigid moralist, showed himself compliant to the will of the emperor by reinstating the excommunicated priest Joseph.
After vain theological disputes, in December 814, there followed personal insults. Nikephoros at first replied to his removal from his office by excommunication, but was at last obliged to yield to force, and was taken to one of the cloisters he had founded, Tou Agathou, and later to that called Tou Hagiou Theodorou. From there he carried on a literary polemic for the cause of the iconodules against the synod of 815; on the occasion of the change of emperors, in 820, he was put forward as a candidate for the patriarchate and at least obtained the promise of toleration.
He died at the monastery of Saint Theodore (Hagiou Theodorou), revered as a confessor. His remains were solemnly brought back to Constantinople by the Patriarch Methodios on March 13, 874, and interred in the Church of the Holy Apostles, where they were annually the object of imperial devotion. His feast is celebrated on this day both in the Greek and Roman Churches; the Greeks also observe 2 June as the day of his death.
Compared with Theodore of Stoudios, Nikephoros appears as a friend of conciliation, learned in patristics, more inclined to take the defensive than the offensive, and possessed of a comparatively chaste, simple style. He was mild in his ecclesiastical and monastical rules and non-partisan in his historical treatment of the period from 610 to 769 (Historia syntomos, breviarium).
His tables of universal history (Chronographikon syntomon), in passages extended and continued, were in great favor with the Byzantines, and were also circulated outside the Empire in the Latin version of Anastasius Bibliothecarius, and also in Slavonic translation. The Chronography offered a universal history from the time of Adam and Eve to his own time. To it he appended a canon catalog (which does not include the Revelation of John). The catalog of the accepted books of the Old and New Testaments is followed by the antilegomena (including Revelation) and the apocrypha. Next to each book is the count of its lines, his stichometry, to which we can compare our accepted texts and judge how much has been added or omitted. This is especially useful for apocrypha for which only fragmentary texts have survived.
The principal works of Nikephorus are three writings referring to iconoclasm:
Nikephoros follows in the path of John of Damascus. His merit is the thoroughness with which he traced the literary and traditional proofs, and his detailed refutations are serviceable for the knowledge they afford of important texts adduced by his opponents and in part drawn from the older church literature.