Žemaitis was born to Jonas Žemaitis and Petronėlė Daukšaitė. Despite the fact that his father was non-religious, Žemaitis was christened in Palanga's church. From 1910 to 1917, he lived with his parents in Łomża, Poland, where his uncle A. Daukša owned a large dairy farm. In Łomża, Žemaitis attended a primary school while his parents were working. In 1917, Žemaitis returned to Lithuania and settled down in the village of Kiaulininkai, near Šiluva, where his grandparents lived. In 1921, he finished first class at the Raseiniai Gymnasium. In 1926, started studying at the War School of Kaunas. In 1929, he finished this school and became a lieutenant. Žemaitis started his military Service with the 2nd Artillery Battery as a commander. In 1936–1938, Žemaitis studied at the School of Applied Artillery in Fontainebleu, France. After the studies, Žemaitis was promoted to captains and commanded artillery units of the Lithuania military forces.