He was a prominent politician of the Socialist Unity Party (SED) in the German Democratic Republic (East Germany).

In the 1920s, he was one of the most prominents members of the KPD, and was head of the Roter Frontkämpferbund in Berlin.

In 1934, he was sentenced to three years of prison, being charged with "conspiracy to commit high treason.

"[1] After World War II, he became active in communist politics in the Soviet Occupation Zone, and was president of the Free German Trade Union Federation (FDGB) 1946-1948, First Secretary (head) of the East Berlin SED district from 1948 to 1953.

Jendretzky famously denounced the Freedom Bell in western Berlin, a gift from Americans as a sign of the fight against communism in Europe, as the "death bell", warning: "The rope of the death bell will become the gallows rope for those who ring it.