After a brief term as procurator of his order, he was attached in 1565 to the papal legation to Spain headed by Cardinal Ugo Boncampagni (later Pope Gregory XIII) which was sent to investigate a charge of heresy levelled against Bartolomé Carranza, Archbishop of Toledo. The violent dislike which Peretti conceived for Boncampagni had a marked influence on his subsequent actions. He hurried back to Rome upon the accession of Pius V, who made him apostolic vicar of his order and then, in 1570, cardinal.
After a brief term as procurator of his order, he was attached in 1565 to the papal legation to Spain, headed by Cardinal Ugo Boncampagni (later Pope Gregory XIII) which was sent to investigate a charge of heresy levelled against Bartolomé Carranza, Archbishop of Toledo. The violent dislike which Peretti conceived for Boncampagni had a marked influence on his subsequent actions. He hurried back to Rome upon the accession of Pius V, who made him apostolic vicar of his order and then, in 1570 cardinal.