He served in the Italian Wars, and was later appointed Viceroy of Valencia where he fought the rebel Germanies in the Revolt of the Brotherhoods.
Diego was the second son of Cardinal Pedro González de Mendoza and Mencia de Lemos (of the House of the Lords of Trofa, in Portugal),[1] making him a member of the powerful Mendoza family.
He played an important role in the Battle of Ruvo and in the taking of Melito in the Kingdom of Naples, for which he was appointed Count of Mélito in 1506.
Mendoza and the government fled into the countryside, and the open warfare phase of the Revolt of the Brotherhoods began.
Mendoza was initially defeated by the agermanats at the Battle of Gandia in June 1521, but royalist troops triumphed elsewhere, and he eventually returned with reinforcements into the city of Valencia in November 1521.