In 1915, he graduated from Peterhof Military School, and participated in World War I. In July 1917, Parts joined the Estonian national units. During the German occupation in 1918, he organized the underground Estonian Defence League. In the Estonian Liberation War, Karl Parts led and organized the armoured trains, and in April 1919, became the commander of the Armoured Trains Division. He commanded in the biggest armoured conflict of war that resulted in the capture of Pskov. After the war, Parts served as commander of the Armoured Trains Brigade from 1921–1923, and later as inspector. He actively participated in defeating the 1924 coup attempt. In 1925, he retired and became a farmer. In 1940, Soviet occupation authorities arrested Parts, and he was shot in imprisonment the year after.