Gabriele Condulmer was born in 1383 to a noble Venetian family — nephew of Pope Gregory XII (Angelo Correr, pope 1406–1415, last pope of the Roman-obedience during the Great Western Schism). Educated in canon law, he entered the Augustinian Canons Regular and rose in the papal court.
Elected Pope on March 3, 1431, taking the name Eugene IV, his sixteen-year pontificate was marked by two principal institutional achievements and one great crisis:
1. The Council of Ferrara-Florence (1438–1445) — the fifteenth ecumenical council, convoked by Eugene IV to undertake the reunion between the Latin-Catholic Western Church and the Greek-Byzantine Eastern Church.
The Byzantine Emperor John VIII Palaeologus personally attended the Council with the entire Byzantine imperial-ecclesiastical delegation — including the Patriarch Joseph II of Constantinople and the principal Byzantine theologians (Mark of Ephesus, Bessarion, Isidore of Kiev, Gemistus Plethon).
On July 6, 1439 at Florence, Eugene IV promulgated the Bull 'Laetentur Coeli' — the solemn definition of the Union between the Latin-Catholic Western Church and the Greek-Byzantine Eastern Church, addressing the three principal doctrinal disputes: the Filioque, the primacy of the Pope, and the Eucharistic doctrine. The union was signed by all the Greek bishops except Mark of Ephesus.
The Union of Florence institutionally represented the most successful medieval Catholic-Orthodox reunion attempt — the union lasting years longer than the earlier Second Council of Lyon (1274) attempt.
Similar union-decrees were negotiated at the Council of Florence with the Armenians (1439), the Jacobites/Copts (1442), the Chaldeans/Nestorians (1445), and the Maronites — producing the most comprehensive medieval Catholic ecumenical reunion.
2. The Council of Basel-Ferrara-Florence conciliar dispute (1431–1449) — the continuing dispute between Eugene IV and the Council of Basel (1431–1449, the continuation of the Council of Constance that had ended the Great Western Schism in 1417), over the conciliarist versus papal-supremacy institutional question.
Eugene IV successfully suppressed the Basel conciliarist party by the 1449 dissolution — institutionally establishing the papal-supremacy institutional principle that would shape the Catholic institutional-theological tradition to the First Vatican Council (1870) and beyond.
3. The continuing Great Western Schism crises — with the antipope Felix V (Amadeus VIII of Savoy) elected by the Basel party in 1439, the Schism lasting until 1449.
Eugene IV died at Rome on February 23, 1447. Though the Union of Florence was repudiated by the Byzantine ecclesiastical-popular reaction in Constantinople in the years after Eugene's death (definitively after the 1453 Ottoman conquest of Constantinople), the Eugenian Union institutionally underpinned the Eastern Catholic Churches — the Catholic Byzantine-rite communities (Melkites, Ukrainians, Ruthenians, Romanians, Bulgarians, Greeks) that would emerge from the particular unions with Rome (the Union of Uzhorod 1646, the Union of Brest 1596, the particular unions of the 17th–20th centuries).