After 1907, Przedpełski belonged to the PPS-Left. In 1914 he was arrested in the Kingdom of Poland and deported to the Tobol Province. In the years 1917-1919 he was active in the Polish independence movement in Russia. In 1919, he returned from exile and fought as a volunteer in the Defense of Lwów, where he earned a number of military distinctions. In January 1920 he became the president of the board of the Brotherly Help (Bratnia Pomoc) at the Polytechnic in Lviv. He co-organized the Polish Military Organization in Upper Silesia, and participated in the Silesian Uprisings.