Karl Amadeus Hartmann was born on 2 August 1905 in Munich. He was the youngest son of the teacher and painter Friedrich Richard Hartmann and his wife Gertrud Hartmann. Early, he got in touch with art and music. In 1919, he started a teachers training course, but dropped out after three years. From 1924-1929 he studied trombone and composition with Joseph Haas at the Staatlichen Akademie der Tonkunst. In the context of the Opera Studios of the Bavarian State Opera, established by Clemens von Franckenstein, as well as in the venue of the avant-garde society of artists named "Die Juryfreien" (The Juryless), Hartmann was able to introduce his first compositions to the public. Among the works performed there are the chamber opera Leben und Sterben des heiligen Teufels (one of five chamber operas which Hartmann combined under the title Wachsfigurenkabinett), the Jazz-Toccata and –Fuge (1928), the Sonatine for piano (1931), the Tanzsuite for wind quintet (1931), the Burleske Musik for wind, percussion and piano (1931) and the Kleine Konzert for string quartet and percussion (1932).These early pieces show influences of jazz and dadaism, of the persiflage technique and the Neue Sachlichkeit.

In 1933, he met conductor Hermann Scherchen, with whom Hartmann held a friendly relationship throughout his life. The 1. String Quartet (1933), which he dedicated to Scherchen, reflects the political situation of the Nazi take-over through the presence of a Jewish folksong which intersperses the piece. From now on Hartmann used composing to take part of the oppressed; his music is a commitment to humanity. Especially melodies with Jewish influences pervade the following symphonies and the opera Simplicius Simplicissimus. Motivation and conception of this opera after Grimmelshausen derived from Scherchen. The expressive musical language contains contrasting elements such as folksong, choral, psalm-like recitative and symphonic episodes. The work deals with the dignity of a single human being who is confronted with a world full of atrocities. It also establishes a relationship between the Thirty Years’ War and the age of fascism. "Lamentably, the world today finds itself in a condition, which is yet making us able to sympathise with the trouble, the fear and the mourning at that time. If you show the world its reflection so that it recognises its horrible face, it might change its mind one day. In spite of all the political thunderclouds I do believe in a better future: this is the idea of the apotheosis in the end." (Hartmann, "Kleine Schriften").

Hartmann understood his following compositions as a personal statement against the prosecution and oppression in Germany during the Nazi time. He dedicated his first orchestral work MISERAE to the prisoners of the concentration camp in Dachau, his 1. Sinfonie with the words of Walt Whitman is subtitled Versuch eines Requiems (Attempt of a Requiem).

In 1934, Hartmann married Elisabeth Reussmann; a year later his son Richard was born. At the IGNM-Festival in Prague 1935, Hartmann received international acknowledgement with MISERAE. In 1936, he won the first prize with his 1. String Quartet at the Geneva Chamber Music Association Carillon.

Moreover, the violin concerto Concerto funebre (1939) became a work of commitment, which Hartmann wanted to be understood as a claim and accusation, as an expression of hopelessness for the mind and, yet in spite of all this, as the never abandoned confidence in the future.

In 1941/42, Hartmann took private tuition with Anton Webern in Vienna. The fascination of the highly constructional yet densely emotional music of Webern’s compositions influenced strongly Hartmann’s further works. The fusion of construction and expression became a significant element of his composing process.

From 1941-43, he worked on his great orchestral tryptichon Sinfoniae Dramaticae, consisting of the Symphonischen Ouverture "China kämpft", the Symphonischen Hymnen and the Symphonischen Suite "Vita Nova" after the poem of same denominator by Percy Bysshe Shelley. Towards the end of the war, Hartmann witnessed how a stream of prisoners were chased out of the concentration camp in Dachau so that they could not be rescued by the confederates who had entered Germany by then. He processed this experience in his Sonata "27. April 1945" for piano, adding the following preface:

"On 27 and 28 April 1945 a stream of 20.000 Dachau prisoners dragged themselves past us. Endless was the stream. Endless was the suffering. Endless was the misery."

The sonata reaches the limit of what is playable and therefore fathoms all the technical as well as emotional extremes. Its musical language oscillates between mourning, accusation, rage and despair and bears witness to Hartmann’s deeply sensed humanity, his humane engagement and his sympathy with the suffering victims of National Socialism.

His 2. String Quartet, which he finished after the war, makes use of the regained freedom and connects to abandoned traditions which had been suppressed by the Third Reich, especially the works of Bartok and Kodalys. In 1945, the dedicated regime-opponent with international reputation was appointed musical dramaturge at the Bayerische Staatsoper. It was his special task to restore the interest in the so far ignored contemporary music and to rehabilitate significant works of the twentieth century into the concert life of the city. Until his death, Hartmann conducted the Musica-Viva-Concerts, the origin of which derived from the effort to familiarise the audience not only with classical modern works, but also with the latest, challenging music of young, aspiring composers. These concerts became a role model for numerous similar events at home and abroad.

At the same time, Hartmann revised various works of his and brought the first four symphonies to their final forms.

From 1948, the number of performances and therefore Hartmann’s recognition in Germany increased constantly, so that he was finally awarded the Musikpreis of the city of Munich in March 1949. This was followed by the Kunstpreis of the Bayrische Akademie der Schönen Künste (1950), the Arnold Schönberg Medal of the IGNM (1954), the Große Kunstpreis of the Land Nordrhein- Westfalen (1957), as well as the Ludwig Spohr Award of the city of Braunschweig, the Schwabing Kunstpreis (1961) and the Bavarian Medal of Merit (1959). In addition, Hartmann became a member of the Academy of Arts in Munich (1952) and Berlin (1955) and received an honorary doctorate from the Spokane University in Washington (1962).

His Symphonie Concertante or 5. Symphonie, which he accomplished in 1951, obtained its musical material from the concept of an earlier composition, the 1933 Concertino for trumpet and wind chamber orchestra. In the context of a commission of the Bayrischer Rundfunk, Hartmann changed his symphony L‘Œuvre after Zola to the 6. Symphonie, which had its world premiere in 1953.

In his Konzert für Klavier, Bläser und Schlagzeug, which likewise had its world premiere in 1953, Hartmann for the first time carried out Boris Blacher’s principle of variable measures (1950). He also applied this technique in his next composition Konzert für Bratsche mit Klavier (1955).

In preparation for his 7. Symphonie, Hartmann increasingly occupied himself with counterpoint techniques, and pored over the works of the ancient Netherlands as well as the works of Johann Sebastian Bach, which bridge to the techniques of Schönberg or Webern. Again, Hartmann tried to connect polyphone counterpoint with expression, by putting side by side polyphonic parts, variation and concerto-like parts on the one hand and lyrical-dramatic moments on the other hand.

In 1959, Hartmann became co-editor of the Schott magazine Neue Zeitschrift für Musik, in spite of his numerous obligations and commissions. The world premier of his last completed commission, the 8. Symphonie, took place 1963 in Cologne. It excels not only in the comparative shortness and reduction of statement, but also in a delight for sound experiments, which was until then unprecedented in Hartmann’s works. The two movements of this work, Cantilène and Dithyrambe Scherzo-Fuga, are merged with a seamless transition and have the same thematic material. Despite their contrasting character, both movements show a preference for imitation and the principle of continuous variation. The last movement with elements from scherzo, fugue and finale, based on the same material, gives the impression of a merging synopsis of all of Hartmann’s symphonic works. After the completion of the 8. Symphony, Hartmann turned towards the opera again, after having rejected numerous attempts. In 1960-61, he contributed the middle movement Ghetto to the cycle Jüdische Chronik, a joint work with Henze, Blacher, Dessau and Wagner-Régency. It was a threnody to the last hours of the Warsaw ghetto.

Up to his last months, Hartmann worked on the Gesangsszene für Bariton und Orchester zu Worten aus "Sodom und Gomorrha" von Jean Giraudoux, which remained unaccomplished, but was published posthumously. In 1963, Hartmann was invited to the North Carolina Music Society, where he was to be appointed Honorary Director.

He died on 5 September 1963 in Munich.