St. Photios was also known for his brilliance and for his missionary zeal, and one of his greatest achievements was in the field of mission work.  In 863, St. Photios sent his two nephews from Thessaloniki, known to us today as Saints Cyril and Methodios, to preach the Gospel in Moravia.  He blessed St. Cyril in his work of developing an alphabet for the Slavonic people, and for the later work of St. Cyril and his brother St. Methodios as missionaries to the Slavs.  As a result of efforts they initiated, the Slavic peoples and nations embraced Orthodox Christianity.

As a Father of the Church, his achievements as Patriarch have earned him a reputation as the greatest of all Patriarchs.