(3 Mar. 1431–23 Feb. 1447)
On Martin V's death the cardinals, resentful of his harsh yoke, all undertook that whoever should be elected would not only devote himself to reform at the impending council at Basle, but would accept the full collaboration of the sacred college in the government of the church and the papal state. Their choice fell on Gabriele Condulmaro, born of wealthy bourgeois parents at Venice c.1383, who as a young man with some friends founded the house of Augustinian canons of San Giorgio in Alga in the lagoon. His uncle Gregory XII promoted him bishop of Siena in 1407 even though he was not yet of canonical age, and then cardinal priest of San Clemente at his controversial creation of 12 May 1408. After Gregory's abdication (4 July 1415) he took part in the council of Constance (1414–18), and Martin V appointed him governor of the March of Ancona and of Bologna, where he successfully re-established papal authority. Once elected, he published a bull confirming the electoral pact which brought the cardinals into the government of the Church, although he was to pay little heed to it during his stormy pontificate.
Eugene first moved against the Colonna family, forcing them to disgorge vast teritories which Martin V had granted to his nephews; his violent measures produced lasting troubles in all parts of the papal state, and made the Colonna his lifelong enemies. But the continuous shadow over his reign was the reform council of Basle, which Martin V had summoned, for which he himself confirmed Cardinal Giuliano Cesarini (1444) as legate, and which was opened in Cesarini's absence by papal representatives on 23 July 1431. The initial attendance was sparse and this, combined with profound mistrust of its intentions, caused Eugene to dissolve it on 18 Dec. 1431, promising a new council to be presided over by himself in eighteen months time in Bologna when the Greeks could be present. His precipitate action created consternation at Basle, shocked Cesarini, and alienated opinion generally. The council refused to disperse, on 15 Feb. 1432 appealed to the teaching of the council of Constance that a general council is superior to a pope, and on 18 Dec. 1432 issued an ultimatum to him. As only six of the 21 cardinals were on his side, schism seemed inevitable, but it was averted largely through the mediation of the German king Sigismund (1410–37), whom Eugene crowned emperor at Rome on 31 May 1433. But he had to withdraw his bull of dissolution (15 Dec. 1433) and acknowledge the council's legitimacy and unbroken continuance in humiliating terms.
At home Eugene faced a chaotic situation, with the condottiere Francesco Sforza occupying the papal state, and a revolution fomented by the vengeful Colonna breaking out in Rome in May 1434. Disguised but still pelted by the crowd, he fled from Sta Maria in Trastevere, where he had taken refuge, to Florence, where he arrived on 23 June and where he mainly resided until 1443; it was a stay which brought him and the curia into touch with the artistic and intellectual aspirations of the Renaissance. Meanwhile his concessions to the council had only whetted its appetite for radical solutions. While carrying through some much needed reforms, it decreed (9 June 1435) the suppression of annates and other papal dues, and set about cutting both papacy and curia down to size. Eugene denounced its pretensions in a memorandum circulated in June 1436 to Christian princes, but it was over union with the eastern church, an item on the council's agenda to which both he and it attached importance, that the final rupture came. While the great majority of the council proposed Basle itself or Avignon or Savoy for the negotiations, Eugene preferred a city in Italy. Having won over the Greeks, he transferred the council on 18 Sept. 1437 to Ferrara. He opened it there through his legate Cardinal Albergati on 8 Jan. 1438, but moved it because of an alleged danger of plague (really for financial reasons) to Florence in Jan. 1439. Here an act of union between the two churches, destined to be ephemeral but forced on the Byzantine emperor John VIII Palaeologus (1425–48) by the imminence of a Turkish invasion, was promulgated in the decree Laetentur coeli on 6 July 1439. Later Eugene signed agreements, on the basis of orthodoxy, with the nominally monophysite Armenians in 1439, with the Copts or Jacobites of Egypt in 1443, and with certain hitherto dissident Nestorian groups in Mesopotamia in 1444 and in Cyprus in 1445; but a crusade he financed in 1443 ended disastrously at Varna, in Bulgaria (10 Nov. 1444), Cardinal Cesarini being among the victims.