Danneberg was one of the architects of Red Vienna and he was killed in the Auschwitz concentration camp in 1942. He joined SDAPÖ and the Workers Youth Association in 1903. In the same year, he became responsible for the educational and cultural programmes of the party and took on the editorship of the SDAPÖ educational journal Die Bildungsarbeit.
In 1909 Danneberg obtained a doctorate in Law.
During the First World War, Danneberg belonged to the "Anti-War left" inside SDAPÖ. Nevertheless, he opposed division of the party and the launching of the Communist Party of Austria.
Danneberg married Gertrud Schröbler in 1918. They had two children together.
Danneberg was a parliamentarian between 1919 and 1934.
Moreover, he became the president of the Vienna Provincial Assembly. Danneberg was also influential in the municipal government of Vienna. As the author of the housing policy of the Vienna SDAPÖ and a co-author of its municipal and taxation policies, he played a pivotal role in shaping "Red Vienna".
Danneberg was arrested and jailed after the Austrian Civil War in 1934.
He was, however, released the following year. After the Anschluss, Danneberg tried to flee to Prague by train, but was arrested again.
He was interned in three different concentration camps. Dachau, Buchenwald and Auschwitz.
He was killed in Auschwitz in 1942.
Danneberg was active in the international youth movement, and became the Secretary of the International Union of Socialist Youth Organisations in 1908. He represented the SDAPÖ in the Executive of the Labour and Socialist International between October 1931 and December 1935.