(5(?) June 824–27(?) Aug. 827)
Disturbances lasting several months followed the death of Paschal I, the nobility and the clerical bureaucracy making rival nominations, but after prolonged discussions the monk Wala (c. 755–836), trusted adviser of Emperor Louis I the Pious (814–40) and his son Lothair I (840–55), pushed through the election of the candidate favoured by himself and the nobility, Eugene, then archpriest of Sta Sabina on the Aventine. Eugene at once not only notified the Frankish court but, going further than his predecessors, acknowledged the emperor's sovereignty in the papal state and swore an oath of loyalty to him.
In late August 824 Louis sent Lothair to Rome to restore order after the troubles of the previous reign and to establish a constitutional relationship between the empire and the papal state which would exclude arbitrary excesses like Paschal's. With the pope's cooperation he made proper provision for the widows and children of persons assassinated under Paschal and decreed the return of exiles. More far-reaching was the ‘Roman constitution’ which he published, again with Eugene's agreement, on 11 Nov. 824, which marked the high point of Frankish control of the papacy. This granted, first, immunity to all persons under either imperial or papal protection. Secondly, it provided that ordinary citizens should be judged by Roman, Frankish, or Lombard law according to their choice. Thirdly, with the object of keeping a tight rein on the pope's administration of Rome, it set up a supervisory commission consisting of one imperial and one papal delegate which would report annually to the emperor. Lastly, it restored the ancient tradition, suspended since Stephen III's synod of 769, by which all the people of Rome as well as the clergy took part in papal elections, stipulating that before being consecrated the pope-elect should take an oath of loyalty to the emperor before the imperial legate. The emperor's sovereignty over the papal state was emphasized by the oath of allegiance which all citizens were to take.
Eugene held an important synod in the Lateran in Nov. 826 at which these rules for elections were ratified. But if he had to show deference to the court in temporal matters, in the spiritual field he asserted an independence which his predecessors had lost under Charlemagne (768–814). Thus, while adopting the Frankish legislation for proprietary churches (i.e. churches with a secular or spiritual proprietor who claimed to control them), the synod published a collection of reforming disciplinary canons (dealing with simony, the qualifications and duties of bishops, clerical education, monastic arrangements, Sunday observance, marriage, etc.) which were extended to the Frankish church. Again, when Louis sent envoys to Rome in 824 to persuade the pope to accept a compromise on sacred images, Eugene firmly insisted that the question had been settled in favour of image veneration by the second council of Nicaea (787). Iconoclasm had flared up afresh at Constantinople under Emperor Leo V (813–20), and his successor Michael II (820–29), whose attitude was one of reserve, had enlisted the help of Louis in approaching Rome, knowing that the Frankish position was that, while images were permissible, they were not to be adored. On 1 Nov. 825, with Eugene's consent, Louis convened a commission of Frankish theologians at Paris to examine the issues, and this duly produced a report rejecting Nicaea II and censuring the pope for protecting error and superstition; but nothing could induce Eugene to budge. It is significant that Louis did not put pressure on him, but left the final decision to him.