Ona Brazauskaitė was born on 9 September 1883 in the village of in the Anykščiai Parish of the Russian Empire to Jadwiga ("née" Michalowska, also known as Jadvyga Mikalauskaitė) and Gustavas Brazauskas (Gustaw Brzezowski). Her parents met when Brazauskas was imprisoned for his participation in the 1863 uprising against Russian rule with Jadwiga's father. Of noble heritage, her family of eight children spoke Polish at home but were divided on whether they identified as Lithuanian or Polish. Brazauskas advocated for a unified Lithuanian and Polish state and distributed books in the Lithuanian language, a banned activity at the time.