Kortner was born in Vienna as Fritz Nathan Kohn into a Jewish family.

After graduating, he joined Max Reinhardt in Berlin in 1911 and then Leopold Jessner in 1916.

He originally gained attention for his explosive energy on stage and his powerful voice; but as the 1920s progressed, his work began to incorporate greater realism, as he opted for a more controlled delivery and greater use of gestures.

With the coming to power of the Nazis, Kortner fled Germany in 1933 with his wife, actress Johanna Hofer, returning first to his native Vienna and, from there, on to Great Britain, and finally, in 1937, to the United States,[1] where he found work as a character actor and theater director.

He returned to Germany in 1949, where he became noted for his innovative staging and direction of classics by William Shakespeare and Molière, such as a Richard III (1964) in which the king crawls over piles of corpses at the finale.