He was arrested at a student meeting in 1902 for advocating Lithuanian causes and served part of a two-year sentence, but succeeded in regaining admission to the university.

After returning to Vilnius, he became involved in the independence movement, frequently contributing articles to periodicals and later working with the War Relief Committee.

On 31 January 1920, Mykolas Biržiška wrote in Lietuvos aidas:the issue of belonging to a certain nationality is not decided by everyone at will, it is not a matter that can be resolved according to the principles of political liberalism, even one cloaked in democratic slogans.

In summer 1921 he landed in court for an article in newspaper "Straż Litwy", and was defended by attorney Tadeusz Wróblewski.

His father, the physician Antanas Biržiška, declined a professorship at the University of Moscow to practice medicine in the rural areas of Lithuania.