In 1780 he joined the Polish Army with the rank of Rotmistrz of Cavalry. On 23 December 1788 he bought from general Aleksander Mycielski the rank of General and the command of 10th Regiment of Foot. That regiment, known as the 'Radzyński Regiment' (of the Ordynacja Rydzyńska) under his command became known as 'Działyński Regiment'. He was a deputy for the famous Sejm Wielki, where together with Jan Kiliński he was one of the leaders of the 'moderate' faction, supporting the King Stanisław August Poniatowski, Polish Constitution of 3 May 1791, and advocating strengthening of the army, enfranchisement of the burghers and alliance with Revolutionary France. The following year together with his regiment he took part in the ill-fated War in Defense of the Constitution (Battle of Swisłocz, Battle of Zelwa on 4 July, Battle of Izabelin on 5 July, Battle of Piaski, Battle of Granne and Battle of Krzemień on 24 July).