Borromeo founded the Confraternity of Christian Doctrine and was a leading figure of the Counter-Reformation together with Ignatius of Loyola and Philip Neri.

At this time his paternal uncle Giulio Cesare Borromeo turned over to him the income from the rich Benedictine abbey of Sts.

Borromeo made plain to his father that all revenues from the abbey beyond what was required to prepare him for a career in the church belonged to the poor and could not be applied to secular use.

Due to a slight speech impediment, he was regarded as slow but his thoroughness and industry meant that he made rapid progress.

[3] Shortly thereafter, on 31 January 1560, the pope created him cardinal, and thus Borromeo as cardinal-nephew was entrusted with both the public and the privy seal of the ecclesiastical state.

[6] After the death of his uncle, Pius IV (1566), Borromeo sent a galley to fetch Cardinal Ugo Boncompagni, the Nuncio in Spain, but he did not arrive in time to be considered at the conclave.

Ghislieri was elected and took the name Pius V.[8] Before Borromeo went to Milan, while he was overseeing reform in Rome, a nobleman remarked that the latter city was no longer a place to enjoy oneself or to make a fortune.

"Carlo Borromeo has undertaken to remake the city from top to bottom," he said, predicting that the reformer's enthusiasm "would lead him to correct the rest of the world once he has finished with Rome.

In addition, he founded the fraternity of Oblates of St. Ambrose, a society of secular men who did not take orders, but devoted themselves to the church and followed a discipline of monastic prayers and study.

[10] The new archbishop's efforts for catechesis and the instruction of youth included the initiation of the first "Sunday School" classes and the work of the Confraternity for Christian Doctrine.

The archbishop carried on his person a small picture of John Fisher, who with Thomas More had been executed during the reign of Henry VIII and for whom he held a great veneration.

During the 19th century Catholic restoration in England, Nicholas Wiseman was to institute an order of Oblates of St Charles, led by Henry Edward Manning, as a congregation of secular priests directly supporting the Archbishop of Westminster.

The Catholic Encyclopedia relates: "In November [1583] he began a visitation as Apostolic visitor of all the cantons of Switzerland and the Grisons, leaving the affairs of his diocese in the hands of Monsignor Owen Lewis, his vicar-general.

[16] Reacting to the pressure of the Protestant Reformation, Borromeo encouraged Ludwig Pfyffer in his development of the "Golden League" but did not live to see its formation in 1586.

It created severe strains in the Swiss civil administration and caused the break-up of Appenzell canton along religious lines.

[17] Charged with implementing the reforms dictated by the Council of Trent, Borromeo's uncompromising stance brought him into conflict with secular leaders, priests, and even the Pope.

[2] In 1584, during his annual retreat at Monte Varallo, he fell ill with "intermittent fever and ague", and on returning to Milan grew rapidly worse.

He is usually represented in art in his robes, barefoot, carrying the cross as archbishop, a rope around his neck, one hand raised in blessing, thus recalling his work during the plague.

The Catholic sovereigns of Europe – Henry III of France, Philip II of Spain, Mary, Queen of Scots – and others showed how they valued his influence.

Cardinal Baronius styled him "a second Ambrose, whose early death, lamented by all good men, inflicted great loss on the Church."