Given his predisposition to letters, no less than to invective, Franco soon became the secretary of Aretino and, after a few years, he decided to go freelance, offering his services to well-known personages of the day.

He travelled the Italian peninsula offering his services to various gentlemen and lords (Casale Monferrato, Mantua, Cosenza, Naples) arriving in Rome in 1558.

[11] While in Rome he thought of starting the career of writer and libelist, putting his pen at the disposal of the various powerful citizens, from whom he was soon hired to produce eulogies, invectives, licentious sonnets and any other literary product requested at the time, including some pasquinade; but shortly after his arrival, on 15 July 1558 he was arrested in the home of Bartolomeo Camerario, then praefectus annonae, who was also arrested for embezzlement, and Franco remained in prison for eight months.

[5] His great misfortune was to accept a commission from the Apostolic Tax Prosecutor Alessandro Pallantieri, to produce an infamous pamphlet and some pasquinades addressed to Pope Paul IV (Pietro Carafa), for distribution following his death ("Commento sopra la vita et costumi di Giovan Pietro Carafa che fu Paolo IV chiamato, et sopra le qualità de tutti i suoi et di coloro che con lui governaro il pontificato").

Questioned and tortured, Franco confessed to Pallantieri's commission for the creation of the libels against Paul IV and his family, entitled "Commento sopra la vita et costumi di Gio.