[4] In 1467 he fought for the Duke beside Bartolomeo Colleoni against the Medici, returning to Mirandola after the death of his father on 8 November to take over the dukedom.

[5] On the death of Borso on 20 August 1471, Galeotto strengthened his friendship with the new Duke, Ercole I d'Este, by entering into a treaty of alliance.

[6] On 9 January 1476, he joining a coterie of ambassadors sent to Naples to escort his bride, Eleanor of Aragon to Ferrara.

Accused of having betrayed the Venetians, in 1486 he changed his allegiance to the Duke of Milan, Ludovico Sforza, who elected him governor of Parma.

[9] His action led him to be considered a tyrant by contemporaries, including the Dominican friar Girolamo Savonarola, who wrote two letters to him, the second dated 26 March 1496, commending him to reform his ways and to "live as it became a Christian.

[9] He was buried in the Church of San Francesco in Mirandola, despite his excommunication for the usurpation of his brother Antonio, for which he obtained a papal dispensation.