Marcantonio Marcolini was born in Fano on 22 November 1721, the son of Count Pietro Paolo Marcolini and Ana Maria Francesca Ferretti, of the counts of Castel Ferretto.
[1] He graduated from the Collegio di San Carlo in Modena on 22 October 1732; from the Pontifical Ecclesiastical Academy in 1740; and then received a doctorate of both laws from the Sapienza University of Rome on 3 July 1742.
[1] In 1743, he was sent to Paris as papal legate to take the red hat to Cardinal Marcello Crescenzi, Apostolic Nuncio to France.
[1] He became a judge of the Reverend Fabric of Saint Peter's basilica in November 1752, becoming its secretary in December 1756.
[1] Shortly thereafter, Pope Clement XIV made him an Assistant at the Pontifical Throne.