[1] He was the second son of Cristoforo Archinto, whose ancestor Manfredo had helped found the monastery of Chiaravalle near Milan in 1135, and Maddalena Torriani.

His brothers were Giovanni Battista, who was a soldier and an ambassador of the Emperor Charles V, and Alessandro, who became a regional quaestor in the city of Milan.

[6] The Milanese embassy met the Emperor in Naples, where Charles was celebrating the marriage of his daughter Marguerite to Alessandro de'Medici.

[8] Archinto revealed such talents for diplomacy that Pope Paul III named him a Protonotary Apostolic partecipante.

[11] When Paul III set off for Nice to meet Charles V and Francis I of France in an effort to arrange a peace, he took Archinto with him, with the title of Governor of the Court.

He spent six months reforming the city, but he was back in Rome in 1539, and preached the funeral oration for the Empress Isabella, wife of Charles V, who had died on 1 May 1539.

[15] Pope Paul III also sent the Bishop of Borgo San Sepolcro to the Council of Trent, whose meetings had been transferred to Bologna.

[17] On 19 October 1546, by the bull "Cum sicut accepimus", he was transferred to the diocese of Saluzzo,[18] though he was still serving as papal Vicar of the city of Rome.

[19] As the new bishop, Archinto sought to acquire for the episcopal income the properties which had been designated by Pope Julius II when he created the diocese of Saluzzo.

[24] Archinto was appointed Archbishop of Milan, on the recommendation of King Philip II,[25] by Pope Paul IV on 16 December 1556.