Mackiewicz is a Polish surname derived from the name Maciek, a diminutive of Maciej (Matthias).
Similar to other young veterans of the war who entered university without their Matura graduation, also Mackiewicz started his favourite subject of biological sciences at the University of Warsaw and then upon moving to Vilnius continued studies at the Vilnius University, but he never graduated with a degree.
Mackiewicz joined the Polish Military Organisation in 1917 and served as a volunteer in the Polish Army during the Polish-Soviet War of 1919–21.