These Milanese nobles, already prominent in the 12th century, came to be divided in political allegiance and to typify the aristocratic political freelance. Some members opposed the Visconti. Antonio supported the Ambrosian Republic (1447-50). Gian Giacomo (1441-1518) became a famous military commander in French service; previously employed by Louis XI in Brittany, in 1483 he broke with Lodovico Sforza, served Charles VIII and led Louis XII's attacks on Milan (1499-1500). He was made French Governor in Milan and led the League of Cambrai forces to victory against Venice at Agnadello (1509). Though defeated at Novara (1513) he took part in another French victory at Marignano (1515). Highly educated, probably by Giorgio Valla, he commissioned in Milan (c. 1511) an unrealized equestrian statue of himself from Leonardo da Vinci.
Teodoro, of another branch of the family, also served France, rallying its defeated forces after the battle of Pavia (1525). Prominent churchmen of the Trivulzio family who were also French partisans included Gian Giacomo's brother Antonio (Cardinal 1500-08), Scaramuccia, Count of Melzo, a councillor of Louis XII (Cardinal 1517-27), and Agostino (Cardinal 1517-48), who served as papal legate in France and in 1527 was taken to Naples as a hostage of Charles V.