group of magnates planning a (never realized) confederacy. He became a foreign member of the Société des Amis des Noirs. 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. 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. In the words of a Swedish diplomat, L. Engstrom, he was “like a tireless spring”, constantly mediating between the two factions. Due to his association with the reformers, in conservative Rome he became infamous as a staunch supporter of revolutionary ideals and was accused of "democratism". Vatican diplomats criticized the king for hiring such a "revolutionary", but the king defended Piattoli quite vividly. In any case, many such claims were exaggerations or rumours spread by his political enemies: according to one such rumour, Piattoli was alleged to incite crowds in France to kill the king. 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. Between 1790 and 1792, Piattoli was sent on several sensitive diplomatic missions for the king to Berlin and other places. He was involved in the negotiations of the Polish-Prussian alliance. He collaborated with Ignacy Potocki, helping draft many texts connected with Potocki's work in the Sejm, the legislature of the Polish–Lithuanian Commonwealth. He was also an active supporter of Poniatowski's plan for a hereditary succession. 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. 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 played a role in convincing the King to collaborate with the leaders of the Patriotic Party on drafting a constitution. 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.