Mazarin was educated by the Jesuits in Rome, and at the University of Alcalá where he studied law. At Alcalá, he studied with Jerome Colonna, and on his return to Rome c. 1622 he became a captain in the army of the Colonna.
He had considerable diplomatic skills, and in 1629 Pope Urban VIII commissioned him to end the war of the Mantuan succession. He was a vice-legate at Avignon 1632-1634 and 1636-1640. In 1639, he became a French citizen, and he entered the service of King Louis XIII the next year. The pope created him cardinal in 1641, at the king's instigation.
Mazarin succeeded Richelieu as prime minister in 1642. He continued his predecessors policies, and in reality ruled France until his death.