Educated by Jesuits, he later studied at the Szkoła Rycerska (Knight's School, also known as the Cadet Corps) in Warsaw, and later in Paris.

In the aftermath of the battle of Zieleńce, Mokronowski became the fourth person to receive the Virtuti Militari order, after prince Józef Poniatowski, Tadeusz Kościuszko and Michał Wielhorski.

During the insurrection he held the position of commander of the city of Warsaw and the National Forces of the Masovian Duchy (komendant miasta Warszawy i Siły Zbrojnej Księstwa Mazowieckiego).

He was elected to the Provisional Temporary Council (Polish: Rada Zastępcza Tymczasowa), but due to his criticism of Tadeusz Kościuszko he was removed from the political body.

Together with prince Józef Poniatowski, Michał Wielhorski and Eustachy Sanguszko, he formed the core of the "court" faction among the insurrectionists.