After being chosen Captain of Milan, he defeated two papal armies and was excommunicated by Pope John XXII.

In 1322 Galeazzo was named capitano del popolo in Milan, and defeated a Papal-Angevin army at Bassignana.

[3] He was excommunicated by Pope John XXII in March 1323 and unrest in Milan impaired his authority.

[3] With the support of Emperor Louis IV, at Monza Galeazzo defeated an army sent against him by John XXII.

[3] Galeazzo was freed in March 1328[3] and took shelter under the other Ghibelline leader of Italy at the time, Castruccio Castracani.