After 1489, he would spend most of his diplomatic career in England as the papal collector,[2] which allowed him to generate significant profits.
After Castellesi was granted English denization on 29 June 1492, he became the clerk of the papal treasury and the bishopric of Hereford.
With whom Castellesi worked together in the matters of England, Silvestro Gigli soon became his bitter rival with growing open hostility.
Even though Castellesi tried to buy a cardinalate in 1498, his efforts were unsuccessful until Alexander VI made him a cardinal, titled of San Grisogono, on 31 May 1503.
[4] Castellesi bought a vigna in Borgo near the Vatican, where he built a sumptuous palace designed by Donato Bramante: it is now known as Palazzo Torlonia.
[4] Castellesi's cardinalship was revoked in 1518 when he was implicated in Alfonso Petrucci's failed attempt at Pope Leo X's assassination.
Wolsey pressed for Castellesi's position as a collector and a cardinal to be revoked, which was eventually backed by King Henry.
The deprivation of his possessions and titles is primarily attributed to Wolsey's years-long personal vindictiveness against Castellesi.