He was born in Mantua, Italy to an ancient family from Lombardy that had moved to Mantua at the time of marquis Lodovico Gonzaga, a relative of Luigia Gonzaga, mother of Castiglione.
He studied the Classics in Mantua and in Milan, where he was a pupil of Merula and of Calcondila. He practiced the court of Ludovico il Moro and when the latter died, he went back to Mantua, again in the court of Gonzaga. In 1499 he lost his father and succeeded him in the representative duties of the head of a noble family, soon his duties would have included representative offices for the court; for instance, he accompanied his marquis for the arrival in Milan of Louis XII. For Gonzaga he travelled quite often; during one of his missions to Rome, he met Guidubaldo da Montefeltro, duke of Urbino, and in 1504 Gonzaga, although reluctant, allowed him to pass to that court.
Urbino was at that time the most refined and elegant among Italian courts, a real meeting point of culture superbly directed and managed by duchess Elisabetta Gonzaga and her sister-in-law Maria Emilia Pia; among most constant guests Pietro Bembo, Giuliano de' Medici, Ottaviano and Federico Fregoso, Cesare Gonzaga (a cousin of both Castiglione and the duke), and many other men of letters. Notably, guests used to organise intellectual competitions which resulted in an interesting, stimulating cultural life that produced a brilliant litterary activity.
In 1506 Castiglione wrote (and played together with Cosimo Gonzaga) his eclogue Tirsi in which allusively, beyond the figures of three shepherds, he originally depicts the court of Urbino. The work contains echoes of both ancient and contemporary poetry, with recalls Vergil, Poliziano, Sannazzaro.
Castiglione wrote about his works and of those of other guests in some letters to other princes, mantaining an activity very near to diplomacy, though in a litterary form, like with Ludovico da Canossa.
Francesco Maria della Rovere succeeded Guidubaldo at his death, and Castiglione remained at his court; with Francesco Maria he will take part to Pope Julius II's expedition against Venice and this made him deserve the title of Novellata, a county near Pesaro. When Pope Leo X was elected, Castiglione was sent to Rome as an ambassador of Urbino. In Rome he shared friendship with many artists and writers; among these, Raphael soon became a really close friend of him, frequently asking for his suggestions. Raphael gratefully painted a famous portait of Castiglione that now is at Louvre (Paris).
In 1516 Castiglione was back in Mantua, where he married Ippolita Torelli, descendant of another ancient noble family. He wrote two passionate letters to her, expressing a deep sentiment, but she unfortunately died only 4 years later, when Castiglione was in Rome again as an ambassador, this time for Mantuan Dukes. In 1521 Pope Leo X conceded him the tonsura (first sacerdotal ceremony) and here begins Castiglione's ecclesiastical career.
In 1524 Pope Clement VII sent him to Spain as nuncius apostolicus (ambassador of the Holy See) in Madrid, and in this role he followed Charles V to Toledo, Sevilla and Granada. When in 1527 Lansquenets invaded and ruined Rome (Sacco di Roma), the Pope suspected him of "special friendship" for the Spanish emperor: effectively Castiglione should have informed the Holy See about the intentions of Charles V, it was his duty to investigate what Spain was planning against the Eternal City. On the other side, quite outrageously, Alonso de Valdes (brother of Juan de Valdes and the secretary of the emperor) publicly declared that the Sacco was a divine punishment for the too many sins of clergy. Castiglione, in an undoubtedly uncomfortable position, answered both, the Pope and Valdes, in two famous letters from Burgos. Valdes received a very long and severe letter in which the nuncius used hard terms to define the Sacco and Valdes' comments. The Pope received instead a letter (dated December 10, 1527) in which Castiglione dared to underline that several aspects of Vatican politics were ambiguous and contradictory, not at all a valid support in his action of pursuing a fair agreement with the Empire; this lack of coherence in the Church's actions had therefore irritated Charles V, was the sense of his argument.
Against any expectation, he received the excuses of the Pope and great honours by the emperor. Today it seems quite certain that Castiglione had no responsibility in the Sacco, and he had played honestly his role in Spain. Also, a popular story about his death due to remorse found no confirmation: he died by Black Death (plague).
In 1528, the year before his death, the book by which he is most famous, The Book of the Courtier (Il Cortegiano), was published in Venice by Andrea d'Asolo (father-in-law of Aldo Manuzio). The book is based upon Castiglione's times at the court of Duke Guidobaldo Montefeltro of Urbino. It describes the ideal court and courtier, going into great detail about the philosophical and cultured discussions that occurred at Urbino. The book is significant because it defined the perfect Renaissance gentleman. In the Middle Ages, the perfect gentleman was a chivalrous knight who distinguished himself by his prowess on the battlefield. Castiglione's book changed that -- now the perfect gentleman had to be educated in the classics as well. The book was soon translated in Spanish, German, French, and English.
Minor works are less known, yet still interesting. Love sonnets and four Amorose canzoni he wrote with reference to his Platonic love for Elisabetta Gonzaga, with a style that recalls very intensively Francesco Petrarca's through Pietro Bembo's ones. Pre-romantics will find in his sonnet Superbi colli e voi, sacre ruine a focal inspiration, however more written by the man of letters than by the poet. Latin poetries are to be remembered, together with his elegy De morte Raphaellis pictoris (for the death of Raphael), and the other elegy in which he imagined his wife (dead) was writing him. In vulgar prose it is remembered a prologo for Bibbiena's Calandria.
His letters are another point of interest, describing not only the man and his personality, but also details about the famous people he met and frequented, or about his diplomat activity; they are considered very important for political, litterarian and historical studies.