Having obtained he degree of Doctor in utroque jure at the University of Padua, Giovanni Delfino seemed to want to embrace the ecclesiastical state, but was instead initiated into a political and diplomatic career; after having exercised some minor offices in Venice, in 1577 he was appointed podestà and captain of Belluno.

[2] On 18 April 1599, he officially represented Venice at the wedding of Philip III of Spain and Margaret of Austria; and in 1600 at those of Henry IV of France and Marie de' Medici.

Pope Clement VIII decided to assign the diocese to Delfin,[3] to whom he was bound by ties of sympathy and mutual respect, despite the fact that Delfin was not a priest and Venetian law did not allow ecclesiastical offices to be held by persons who had resided at the court of Rome.

[5] Delfino resigned the diocese of Vicenza, after he became a cardinal, in favor of his brother Dionisio Delfini.

[6] Bishop Giovanni Delfino was named a cardinal-priest by Pope Clement VIII on 9 June 1604.