Eugene is described by his biographer as simple and humble, learned and eloquent, handsome and generous, a lover of peace, and wholly occupied with the thought of doing what was pleasing to God.
Eugene's candidacy was endorsed by Abbot Walla, who was then in Rome and served as a councilor to both the current emperor, Louis the Pious, and his predecessor, Charlemagne.
A Constitutio Romana was then agreed upon between the pope and the emperor in 824 which advanced the imperial pretensions in the city of Rome, but also checked the power of the nobles.
At first the iconoclast Eastern Roman Emperor Michael II showed himself tolerant towards the icon worshippers, and their great champion, Theodore the Studite, wrote to him to exhort him "to unite us (the Church of Constantinople) to the head of the Churches of God, Rome, and through it with the three patriarchs" and to refer any doubtful points to the decision of Old Rome in accordance with ancient custom.
But Michael soon forgot his tolerance, bitterly persecuted the icon worshippers, and endeavoured to secure the co-operation of Louis the Pious.
Before taking any steps to meet the wishes of Michael, Louis asked the pope's permission for a number of his bishops to assemble and make a selection of passages from the Fathers to elucidate the question that the Greeks had put before them.
Their collection of extracts from the Fathers was a mass of confused and ill-digested lore, and both their conclusions and the letters they wished the pope to forward to the Greeks were based on a complete misunderstanding of the decrees of the Second Council of Nicaea.
To help in the work of the conversion of the North, Eugene wrote commending St. Ansgar, the Apostle of the Scandinavians, and his companions "to all the sons of the Catholic Church".
As pope, Eugene beautified his ancient church of St. Sabina with mosaics and metalwork bearing his name that were still intact as late as the 16th century.