Italian cardinal, humanist, and lawyer who, upon entering the service of the church in 1510, became one of the most valued representatives of the papacy.

Between 1511 and 1539 five popes employed Campeggio almost continuously as nuncio or legate; his political and religious embassies gave him a particular knowledge of Germany, where he was nuncio to the emperor Maximilian in 1511 and 1513 and legate at the diets of Regensburg (1524) and Augsburg (1530). In Rome his knowledge of curial procedure made him a realistic advocate of reform, though always loyal to the papacy. He first visited England on an unsuccessful mission for Leo X (1518–19), was given the See of Salisbury in 1524, and in 1528 went to England to inquire into the King's marriage with Catherine of Aragon as co-legate with Cardinal Wolsey (Wolsey, Thomas, Cardinal); the case was withdrawn to Rome before a decision had been given. He served on preparatory commissions for the Council of Trent before his death.