Enea Silvio de'Piccolomini, after studying at the universities of Siena and Florence, had settled in the former city as a teacher, but in 1431 had accepted the post of secretary to Domenico Capranica, bishop of Fermo, then on his way to the Council of Basel (1431–39).

Capranica had been protesting against the new Pope Eugene IV's refusal of a cardinalate for him, which had been designated by Pope Martin V. Arriving at Basel after enduring a stormy voyage to Genoa and then a trip across the Alps, Enea had successively served Capranica, who ran short of money, and then other masters.

He had been sent by Cardinal Albergati, Eugenius IV's legate at the council, on a secret mission to Scotland in 1435, the object of which is variously related, even by himself.

He had visited England as well as Scotland, had undergone many perils and vicissitudes in both countries, and has left a valuable account of each.

The journey to Scotland had proved so tempestuous that Piccolomini swore that he would walk barefoot to the nearest shrine of Our Lady from their landing port.

This proved to be Dunbar; the nearest shrine was ten miles distant at Whitekirk.

The journey through the ice and snow had left Aeneas afflicted with pain in his legs for the rest of his life.

It is only once he arrived in Newcastle that he had felt he had returned to a civilized part of the world and the inhabitable face of the Earth, Scotland and the far north of England being "wild, bare and never visited by the sun in winter".

In Scotland, he had fathered his second natural child, the other one having been born in Strasbourg.

Upon his return to Basel, Enea had sided actively with the council in its conflict with the Pope, and, although still a layman, had eventually obtained a share in the direction of its affairs.

He had supported the creation of the Antipope Felix V (Amadeus, Duke of Savoy) and had participated in his coronation.

Enea then withdrew to the court of Holy Roman Emperor Emperor Frederick III court in Vienna.

Crowned imperial poet laureate in 1442, he has obtained the patronage of the emperor's chancellor, Kaspar Schlick.

Some identify the love adventure at Siena that Enea related in his romance The Tale of the Two Lovers with an escapade of the chancellor.

Enea’s character had hitherto been that of an easy and democratic-minded man of the world with no pretense to strictness in morals or consistency in politics.

He now begins to be more regular in the former respect, and in the latter had adopted a decided line by making his peace between the Empire and Rome.

Being sent on a mission to Rome in 1445, with the ostensible object of inducing Pope Eugene to convoke a new council, he had been absolved from ecclesiastical censures and returned to Germany under an engagement to assist the Pope.

This he did most effectually by the diplomatic dexterity with which he had smoothed away differences between the papal court of Rome and the German imperial electors.

He plays a leading role in concluding a compromise in 1447 by which the dying Pope Eugene accepts the reconciliation tendered by the German princes.

As a result, the council and the antipope are left without support.

He had already taken orders, and one of the first acts of Pope Eugene's successor, Pope Nicholas V (1447–1455), is to make him Bishop of Trieste.