Formerly an Augustinian monk, he was a cardinal when unanimously elected to succeed Martin V. His pontificate was dominated by his struggle with the Council (1431–37) of Basel, which assembled to effect church reform. When Eugenius sought to dissolve the council because of its hostility toward the papacy, its members affirmed superiority over the Pope (1433). The conflict between Eugenius and the council eased as a possibility emerged of reuniting the Roman and Greek churches. The Greeks preferred negotiating with the Pope and wished to meet in Italy. Eugenius thus ordered the council to transfer to Ferrara in 1438. Many of the bishops obeyed, but dissidents stayed on at Basel as a rump council, whose members Eugenius excommunicated. They, in turn, promptly “deposed” him.
Meanwhile, on July 7, 1438, King Charles VII of France issued, against Eugenius’ will, the Pragmatic Sanction of Bourges, a pronouncement—prompted by the decrees of the Council of Basel—that established certain liberties for the French Church and advocated restriction of papal power. A plague forced the council at Ferrara to move to Florence, where a union of the Greek and Roman churches (though short-lived) was concluded on July 6, 1439. Eugenius’ success at the Council of Ferrara–Florence enabled him to defy the Basel assembly, thus ending the rump council and restoring papal sovereignty to the church. His efforts to relieve Constantinople following the council were less successful. The Crusade he launched against the Ottomans was defeated at Varna in 1444, foreshadowing the fall of Constantinople in 1453.