Though he began his career as a lawyer and judge in the papal administration, he spent most of his active life travelling as a diplomat in Germany and eastern Europe, attempting to arrange a crusade against the Ottoman Turks.

[9] He worked with Cardinal Nicholas of Cusa, to placate the strong feelings of the German princes against Pope Eugene IV (1383 – 23 February 1447), to overcome their "neutrality" in the last and schismatic phase of the Council of Basel.

The Conclave to elect his successor met at the Church of Santa Maria sopra Minerva in Rome, beginning on 4 March, with eighteen of the twenty-six cardinals in attendance, Juan Carvajal among them.

Cardinal Alain de Coëtivy made a highly inflammatory speech, pointing out that Bessarion was a Greek and perhaps not as orthodox as one might wish in a pope.

[25] In 1455 Carvajal was sent by Pope Callistus III[26] to Hungary to preach a vigorous crusade against the Turks, and for six years was the leader of the first effectual resistance made by Christian Europe to the progress of the Ottoman conquerors of Constantinople (1453).

Tommaso Tommasini, Bishop of Lesina, converted the King from the Bosnian Church to Roman Catholicism between 1445 and 1446,[28] however, only as late as 1457 did Cardinal perform the baptism.

He was still in Hungary when Pope Pius II invited the princes of Christian Europe to meet him at Mantua (1459) to confer on the common danger and the need of a general crusade.

While Cardinal Bessarion sought in Germany something more than brilliant promises, Carvajal continued his labours in Hungary, which he left only in the autumn of 1461, "grown old and feeble", says Pastor,[32] "in that severe climate, amid the turmoils of the Court and the camp, and the fatigues of travel … [in] that bleak country of moorlands and marshes".

In spite of his age and feeble health, he was still willing to take a foremost part in the crusade that Pius II was preparing at Ancona in 1464, when the death of that pope (14/15 August) put an end to the enterprise.

But Pius II, anticipating his possible death during his travels, had issued a decree on 5 January 1459 suspending the regulation of Gregory X and specifying instead that the Conclave should take place in Rome no matter where he died.

Carvajal deeply distrusted him, and believed "that it would be absolutely necessary to employ the knife in the case of wounds which admitted of no other remedy, and to guard against fatal corruption by severing the decayed members from the body of Holy Church.

"[38] By his contemporaries he was considered the ornament of the Church, comparable to her ancient Fathers (Cardinal Ammanati) and the sole reminder of the heroic grandeur of Rome's earliest founders (Pomponius Laetus).

Though genial in intercourse, there was something awe-inspiring about this saintly man whose ascetic life enabled him to provide liberally for the poor and for needy churches.

[39] Frantiãsek Palacký, the historian of Bohemia, writes of Carvajal: "Not only in zeal for the Faith, in moral purity and strength of character, was he unsurpassed, but he was also unequalled in knowledge of the world, in experience of ecclesiastical affairs, and in the services which he rendered to the papal authority.

It was chiefly due to his labours, prolonged during a period of twenty years, that Rome at last got the better of Constance and Basle, that the nations returned to their allegiance, and that her power and glory again shone before the world with a splendour that they had not seen since the time of Boniface VIII.

[42] "Pars hæc vitæ ultima Christo neganda non est" (I must not refuse to Christ this last portion of my life) were the words in which he offered himself to Pius II as leader of a relief to the Republic of Ragusa which was being hard-pressed in 1464 by the Turks.

His discourse in the papal consistories, says Pastor, was brief, simple, clear, logical, and devoid of contemporary rhetoric; his legatine reports have the same "restrained and impersonal character".