After the war, Sindermann returned to Saxony and joined the KPD. After 1946 he was a member of the
Socialist Unity Party (SED), created in April 1946 from the
forced merger of Communists and Social Democrats in the
Soviet Occupation Zone. Sindermann worked as a newspaper editor of the
Sächsische Volkszeitung at Dresden and the
Volksstimme at Chemnitz from 1945 to 1947. He became First party secretary in the
Landkreis of Chemnitz and Leipzig. He ran afoul of party co-chairman
Otto Grotewohl, whom he criticised for being married to a former
Nazi functionary, and in June 1949 was censured by the party's controlling commission and was demoted to the
Freiheit paper in Halle, where he then became editor-in-chief from 1950 to 1953. Sindermann was director of agitation and propaganda in the
Central Committee from 1954 to 1963. In 1958, he became a candidate and in 1963 a member of the Central Committee. In the same year, he also was appointed first party secretary in the district of Halle (until 1971) and was first elected into the
Volkskammer. In 1967, he was admitted to the
Politburo. ==In the East German leadership==