He published and served as the editor-in-chief of the independent Wilno (Vilnius) periodical titled "Słowo," wholly financially supported by the noble families of the former Grand Duchy of Lithuania.

He actively promoted the idea of the so-called Jagellonian Poland, i.e., return to the Polish–Lithuanian Commonwealth style of governance in Eastern Europe.

He supported Józef Piłsudski[2] and in 1928–35 served as a deputy to the Sejm (Poland's parliament), representing the Piłsudskiite Nonpartisan Bloc for Cooperation with the Government.

After Piłsudski's death in 1935, Mackiewicz criticized the ruling elite and in 1939 was imprisoned for 17 days at the Bereza Kartuska detention camp.

He was the older brother of ardent enemy of the communist system, writer Józef Mackiewicz.