After the war, Mączyński settled near Brzeżany and became a social activist. In 1922 he was elected as Deputy to the first Polish parliament (Sejm) as member of the right-wing Christian Union of National Unity coalition from Lwów. He returned to the Army in 1927 at the age of 46 but retired two years later in 1929, and in 1933 was awarded the Cross of Independence with Swords for his service during the Polish–Soviet War. He also published his memoirs and analysis of the battle of Lwów, titled " Boje Lwowskie", with description of the anti-Jewish "Lwów pogrom". Mączyński remained single. Known to local nationalists, he was a target of notable arsons. He died of an illness at the age of 54. His place in the Polish history of Lviv was reasserted only after the collapse of the Soviet Union.