Freed in 1800, he worked several years with Polish and Russian statesman Prince Adam Jerzy Czartoryski in the service of Russia, before retiring to Courland.

[3] Soon he became involved in political activism, and in 1774 he published (anonymously) a brochure titled Saggio intorno al luogo del seppellire, which focused on the issue of hygiene and burials near churches.

[4] During that time he developed extensive contacts at various European courts in Courland, Austria (Vienna), Italy (Turin) and France (Paris).

[4][5] Piattoli developed contacts with notable figures on the Polish political scene, initially from the group opposed to the royal faction.

[4] By the end of his stay in Paris, he likely became a supporter of reforms in France and Poland, and begun taking his first serious steps in political activism, through the involvement in the Quattuowirat, a group of magnates planning a (never realized) confederacy.

[4] Through his freemason contacts with Pierre Maurice Glayre, Piattoli won the confidence of Poland's King Stanisław August Poniatowski, becoming his agent in Paris and, by the end of 1789, his private secretary and librarian, although without any official title.

[6][7] Acting as a sort of cultural aide, Piattoli, who had strong ties to the reformist and often anti-royal opposition, became an important link between the reformers—Ignacy Potocki in particular—and the king.

[7][9] In reality, Piattoli supported the Monarchiens of the French Revolution's early stages, but more in the direction of peaceful transformation into a constitutional republic than the regicidal excesses.

[8] Piattoli, as Poniatowski's secretary and a resident of the Royal Castle in Warsaw, has been credited with winning the King over to the idea of social reforms and with playing a part in the drafting of the Constitution of 3 May 1791.

[12] The exact nature of Piattoli's role in regard to the Constitution remains uncertain; modern historians disagree to what degree he was an executor, a mediator, or an initiator.

He might have prepared or expanded drafts of the document, based on discussions among the principal authors, including the King, Hugo Kołłątaj (another politically active Roman Catholic priest) and Ignacy Potocki.

[12] Historian Emanuel Rostworowski describes him as a vital secretary-editor, who certainly participated in related discussions and influenced both Potocki and the king, and calls Piattoli's quarters in the Royal Palace a "creche" of the constitution.

[10] During the War in Defence of the Constitution in 1792, Piattoli found himself on another diplomatic mission to Dresden, where he stayed after the Commonwealth's defeat at the hands of Imperial Russia resulted in the Second Partition of Poland.

[15] After the failure of the Kościuszko Insurrection later in 1794, many prisoners were set free, but Piattoli was kept imprisoned, together with Kołłątaj, as the Russian authorities insisted that the two were "extremely dangerous".

[15] Hence, even after the final Partitions of the Polish–Lithuanian Commonwealth in 1795, Piattoli was kept interned in Prague by the Austrian Empire authorities until 1800, despite requests for his release from Poniatowski and even Napoleon Bonaparte.

[15] Around that time, he and Czartoryski authored a plan for a European federal organization of states intended to prevent armed conflicts and to maintain perpetual peace.