On 13 March 1775[1] he became an aide to the bishop of Vilnius (titular bishop of Cinna), and on 17 September 1781[2] he became the bishop of Livonia (Polish: Inflanty). At that time he also became administrator of the Courlanddiocese. He is known to have misappropriated vast amounts of the Church's and the public's finances. From 1787 he received a steady pension from the Russian embassy in Poland,[3] becoming a protégé of the Russian ambassador Otto Magnus von Stackelberg. He represented the Russian side in Sejms and local Sejmiks, often bribing or threatening other deputies. With Stackleberg's support he was nominated to the Permanent Council (1782–1786). On 19 December 1791[4] he became the coadjutor bishop of Vilnius with bishop Ignacy Jakub Massalski. His bishop nominations were a reward for his service to the Russian Empire: they were controlled by Empress Catherine the Great, were not consulted with Rome, and served to both reward Russia's loyalists in their dominions, as well as increase the Russian state's control over the Roman Catholic Church there.[5]
In 1786 he published two novels: Ksiądz Pleban (Parish Priest), outlining in literary form a perfect parish of the Age of Enlightenment[6] and Panicz gospodarz (Mister Ruler). A year later, he wrote another novel, Obywatel (The Citizen)[7] He has also translated some plays from French.[8][9] In 1791 he wrote a novel Czarownica (Witch).[9]
In the aftermath of the Warsaw Uprising in April 1794, part of the Kościuszko Uprising, Kossakowski was imprisoned by the revolutionaries. A few days before the start of the uprising, Kossakowski suggested that the Russian troops should surround the churches and arrest all known dissidents. Soon afterwards, Jan Kiliński, one of the leaders of the uprising, presented documents found in the archives of the Russian embassy about Kossakowski's being on the Russian payroll. Most of the citizens of Warsaw, whose support was crucial to the uprising, demanded that Kossakowski and others found to be acting on Russia's behalf against the Commonwealth should be executed. Their stance influenced the revolutionary Criminal Court, and Kossakowski, together with Józef Ankwicz (leader of the Permanent Council) and hetmenPiotr Ożarowski and Józef Zabiełło were convicted of treason and sentenced to hanging on 9 May.[13]
^Jan IJ. van der Meer, Literary Activities and Attitudes in the Stanislavian Age in Poland (1764-1795): A Social System?, Editions Rodopi B.V., 2002, ISBN9042009330, Google Prin, p. 41
^Ángel-Luis Pujante and A. J. Hoenselaars, Four Hundred Years of Shakespeare in Europe, University of Delaware Press, 2003, ISBN0874138124, Google Prin, p. 62