He was a younger brother to the more famous Lithuanian military officer and later statesman Povilas Plechavičius.

[2] Together with his elder brother Povilas, he completed the Cossack Cavalry School in Orenburg [ru].

From December 1918 to February 1919 he actively participated in the fighting against the invading Bolsheviks with partisans in the areas of Seda, Telšiai and Akmenė.

[2][4] After the Soviet Union occupied Lithuania in June 1940, he was arrested by the NKVD on 13 July 1940.

[3] He was brutally interrogated in the prison of Raseiniai, and in July 1941 was deported to the Sol Iletsky in the Chkalov Oblast and in October to Petropavl.

[4] He was awarded the following orders:[4] There is a statue dedicated to Aleksandras Plechavičius in the Kalniškiai village of the Stalgėnai eldership.