In 1519, Antonio took part in the diplomatic meetings headed by Mercurino Gattinara at Montpellier, France, with king Francis I of France representatives.
Nevertheless, when Maximilian's grandson Ferdinand I succeeded him as Archduke of Austria in 1521, his elder brother Emperor Emperor Charles V (1519–1556) appointed Mercurino Gattinara as "Grand Chancellor of all the realms and kingdoms of the king" (Großkanzler aller Länder und Königreiche).
During a review for the purpose of administrative reform, Gattinara advised Charles, in a section of the report entitled “Reverence toward God” on issues such as: whether Moors and Infidels should be tolerated in his lands; whether the inhabitants of the West Indian islands and the mainland were to be converted to Christianity; and whether the Inquisition should be reformed.