He became a general and diplomat for Charles V, Holy Roman Emperor and stayed in the service of his son, Philip II of Spain, serving as Governor of Piombino and as Spanish ambassador to England.

He failed to defend Talamona and Porto Ercole, but in turn repealed the Franco-Turk forces in Orbetello along with Stefano Colonna and the local Spanish tercios, defeating French mercenary general Leone Strozzi.

In 1553, Vitelli was in Corsica serving against Franco-Ottoman invasion, capturing the city of San Fiorenzo against the efforts of Sampiero Corso, but he was recalled to Florence due to the entry of the Republic of Siena into the war.

Vitelli spent the next months taking enemy cities from San Quirico d'Orcia to Scarlino, and helped Gabro Serbelloni defending Piombino from an Ottoman attack.

After Charles V's death, Cosimo sent him as the Tuscan ambassador to the Spanish court, where King Philip II recruited him to expel the French garrison of Montalcino.

[7] When Cosimo retired from governing duties in 1564, his succession by his son Francesco I made Vitelli an uncomfortable member of the old guard in Tuscany, leading him to join Philip II's armies full time.