He was much affected in his early political development by the events of the unsuccessful Workers’ Revolution in Bavaria that followed the collapse of the German empire at the end of World War I (see Bavarian Soviet Republic).

At the Munich Academy in the 1920s, Hartmann studied with Joseph Haas, a pupil of Max Reger, and later received intellectual stimulus and encouragement from the conductor Hermann Scherchen, an ally of the Schoenberg school, with whom he had a nearly lifelong mentor-protégé relationship.

His piano sonata 27 April 1945 portrays 20,000 prisoners from Dachau whom Hartmann witnessed being led away from Allied forces at the end of the war.

[3][better source needed] During World War II, though already an experienced composer, Hartmann submitted to a course of private tuition in Vienna by Schoenberg’s pupil Anton Webern (with whom he often disagreed on a personal and political level).

After the fall of Adolf Hitler, Hartmann was one of the few prominent surviving anti-fascists in Bavaria whom the postwar Allied administration could appoint to a position of responsibility.

Hartmann also involved sculptors and artists such as Jean Cocteau, Le Corbusier, and Joan Miró in exhibitions at Musica Viva.

In 1963, he died of stomach cancer at the age of 58, leaving his last work – an extended symphonic Gesangsszene for voice and orchestra on words from Jean Giraudoux’s apocalyptic drama Sodom and Gomorrah – unfinished.

After the defeat of the Third Reich in World War II, the regime's real victims had become clear, and the cantata's title was changed to Symphonic Fragment: Attempt at a Requiem to honor the millions killed in the Holocaust.

6; probably his most widely known work, through performances and recordings, is his Concerto funebre for violin and strings, composed at the beginning of World War II and making use of a Hussite chorale and a Russian revolutionary song of 1905.

Hartmann attempted a synthesis of many different idioms, including musical expressionism and jazz stylization, into organic symphonic forms in the tradition of Bruckner and Mahler.

[4] Conductors who regularly performed Hartmann's music include Rafael Kubelik and Ferdinand Leitner, who recorded the third and sixth symphonies.