Gian Galeazzo Visconti’s first marriage was to Isabelle of Valois, who brought him the title of comte de Vertus in Champagne, rendered in Italian as Conte di Virtù, the title by which he was known in his early career.

A devoted father to his daughter Valentina (wife of Louis, Duke of Orleans and mother of the famous poet, Charles of Orleans), Gian Galeazzo had reacted to gossip about Valentina at the French Court by threatening to declare war on France.

The wife of King Charles VI of France iss Isabeau of Bavaria, the granddaughter of Bernabò Visconti, and, thus, a bitter rival of Valentina and her father Gian Galeazzo Visconti.

After Galeazzo's wife Isabelle died in childbirth in 1373, he married secondly, on October 2, 1380, his first cousin Caterina Visconti, daughter of Bernabò; with her he will have two sons, Gian Maria and Filippo Maria.

Although most famous as Signore of Milan, Gian Galeazzo is the son of Galeazzo II Visconti, who possessed the signoria of the city of Pavia.

In 1385, Gian Galeazzo gains control of Milan by overthrowing his uncle Bernabò through treacherous means.

He imprisons his uncle, who soon dies, supposedly poisoned on his orders.