The young Mazzarosa was an attentive observer of the events of those years and admired the strict, but moderate regime that was installed with the creation of the Principality of Lucca and Piombino.

At the time of the collapse of the Napoleonic power in Italy, Mazzarosa was chosen by the reconstituted Senate of the Republic to become part of the Provisory Government of the Lucchese States (May 1814).

In fact though power was exercised by the commanders of the Austrian troops who almost immediately fell under the control of the British who had originally occupied the Principate.

Mazzarosa's brother, Ascanio Mansi, served at the highest levels of the duchy's government for decades, occupying the position of secretary of state and often even that of minister of the interior and exterior, respectively.

Mazzarosa, who was interested in various topics including agronomy, took part in the first Congresso degli Scienziati Italiani held in Pisa in 1839 and on that occasion proposed the first general Italian agrarian survey.

In that period in fact Lucca saw the spread of a moderate liberalism that looked for reforms and to some kind of Italian unification, ideally federal in nature.

The duke, whose politics had always been mild and permissive, seemed to hesitate, while Mazzarosa sought to convince him to offer moderate and essentially liberal concessions.