Apitz was born in Leipzig as the twelfth child of a washer woman. During World War I he was a passionate supporter of German Communist Party leader Karl Liebknecht.
He took active part in the German November Revolution of 1918 and the Kapp Putsch of 1920. During the latter he published his first poems and short stories in Communist newspapers. He wrote his first play in 1924 and was later repeatedly imprisoned under Nazi rule in various concentration camps for spreading socialistic anti-war propaganda and being an active member of the Communist Party. From 1937 to 1945 he was an inmate of the Buchenwald concentration camp near Weimar. It was this stay that became the basis for his most famous novel, Nackt unter Wölfen (Naked Among the Wolves).