In June 1542, he became a scriptor of apostolic letters. He completed his training at the Gymnasium of Perugia, studying letters and probably also civil and canon law, and gained the academic title of Magister. Early in his ecclesiastical career, he became a papal chaplain.Through his older brother's influence, Allessandro was able to purchase a post in the Apostolic Camera. He became a canon of St. Peter's Basilica on 18 April 1554.[2]
Around 1549, Sforza came into possession of the garden/vineyard of Cardinal Rodolfo Pio da Carpi on the Quirinal. However, sometime after his death, financial constraints compelled his family to sell it to the Barberini. It became the site of the Palazzo Barberini.
He was caught up in a minor scandal after was he involved in a plan to return two galleys in use by the French to Charles V, Holy Roman Emperor. Pretending to wish to embark, he had the vessels travel from Civitavecchia to Gaeta. The Sforza's were supporters of the Emperor; Pope Paul IV was not. Their actions caused an international outcry. The pope considered this an outrage and had Cardinal Guido Ascanio Sforza arrested in Castel Sant'Angelo. Alexander was dismissed from his posts and lost his ecclesiastical benefits. Imperial diplomacy facilitated an agreement: the return to Civitavecchia of Alessandro, with the galleys, in exchange for the release of his cardinal brother. The solution was accepted, however Sforza landed before reaching his destination and took refuge in the family fiefdom of Santa Fiora. After some cardinals intervened, Alessandro was reinstated in October 1557.[3]
In 1559, Sforza was named a praefectus annonae, charged with supervising the city's grain supply. In April 1560, he was bishop-elect of Parma, although his brother reserved several rights. He became an active participant in the Council of Trent. In 1564, he presided over the diocesan synod in Parma, and oversaw the publication of the Table of Christian Doctrine (in Parma, for Seth Viotti, 1564), a handbook which constitutes an early example of a post-Tridentine catechism.[3] In 1566, he funded the diocesan seminary.[4]
In 1573, he commissioned Giacomo della Porta to complete the family chapel started by his brother at Santa Maria Maggiore.[5] Around 1576, Sforza had a villa built, called "Sforzesca", in Castell'Azzara. It served the cardinal both as a summer residence and as a basis for the repression of the Brigandage. Gregory XIII stayed there in September 1578.
He died suddenly in Macerata on 16 May 1581, aged 46 or 47. He was buried in the Sforza family chapel in the Basilica di Santa Maria Maggiore.[2]