The Council settled the dispute that had broken out after the deposition of
Patriarch of Constantinople in 858. Ignatius, himself appointed to his office in an uncanonical manner, opposed
Bardas, who had deposed the regent
Theodora. In response, Bardas' nephew, the youthful Emperor
Michael III engineered Ignatius's deposition and confinement on the charge of treason. The patriarchal throne was filled with
Photius, a renowned scholar and kinsman of Bardas. The deposition of Ignatius without a formal ecclesiastical trial and the sudden promotion of Photios caused scandal in the church.
Pope Nicholas I and the western bishops took up the cause of Ignatios and condemned Photios's election as uncanonical. In 863, at a synod in Rome the pope deposed Photios, and reappointed Ignatius as the rightful patriarch. However, Photius enjoined the support of the Emperor and responded by calling a Council and excommunicating the pope.
This state of affairs changed when Photius's patrons, Bardas and Emperor Michael III, were murdered in 866 and 867, respectively, by
Basil the Macedonian, who now usurped the throne. Photios was deposed as patriarch, not so much because he was a protégé of Bardas and Michael, but because Basil was seeking an alliance with the Pope and the western emperor. Photios was removed from his office and banished about the end of September 867, and Ignatios was reinstated on 23 November. Photios was condemned by a
Council held at Constantinople from 5 October 869 to 28 February 870. Photius was deposed and barred from the patriarchal office, while Ignatius was reinstated.