Early career

Sieber worked as a forest worker until 1947 and as a forestry assistant until 1948 in Ilmenau. He also became a member and functionary of the FDGB (Free German Trade Union Federation), after which he became a principal clerk in the German Economic Commission.^[1]

In 1948, he joined the ruling Socialist Unity Party (SED) and attended a study program at the Academy for Political Science and Law of the GDR in Potsdam from 1949 to 1950. From 1949 to 1951, he served as a consultant in the Ministry of Planning and until 1952 as a chief consultant in its successor, the State Planning Commission.^[1]

After studying at the "Karl Marx" Party Academy, he served as First Secretary of the SED in the State Planning Commission until 1962, Deputy Chairman of the Central Commission for State Control at the Council of Ministers until 1963, and inaugural First Deputy Chairman of the Workers' and Farmers' Inspection Committee until 1965. Additionally, he was a member of the Central Auditing Commission (German: Zentrale Revisionskommission) (ZRK) of the SED from 1963 to 1967.^[1]

Following distance learning at the SED's Central Institute for Socialist Economic Management, Sieber served as Minister for Trade and Supply from March 1965 to November 1972, succeeding Gerhard Lucht, and as Ambassador of the GDR to the Polish People's Republic from 1973 to 1980. During his diplomatic tenure, he was elected to the Central Committee of the SED as a candidate member.^[1]

SED Central Committee

In December 1980, he was made head of the Department for International Relations of the Central Committee,^[1][2][3] succeeding Egon Winkelmann,^[3] who became Ambassador to the Soviet Union.^[4]

The International Relations Department was responsible for preparing Politburo decisions that concerned foreign policy issues and to control their implementation.^[3] As head, Sieber met foreign leaders, especially leaders of other communist parties and national liberation movements such as SWAPO president Sam Nujoma.

Having been elected as a candidate member in May 1976 (IX. Party Congress), Sieber rose to become a full member of the Central Committee of the SED in April 1981 (X. Party Congress), serving until its collective resignation in December 1989. He additionally became member of the Volkskammer in 1981,^[1] nominally representing a constituency in southern Bezirk Magdeburg.^[5]

In 1964, Sieber was awarded the Patriotic Order of Merit in Silver, in 1979 in Gold,^[6] and in 1988, the Banner of Labor.^[1][7]

Peaceful Revolution

During the Wende, on 8 November 1989, Sieber was elected to the Politburo of the Central Committee of the SED, the de facto highest leadership body in East Germany, as a candidate member and to the Central Committee Secretariat as Secretary responsible for International Politics and Economics.^[1]

Sieber's career advancement would prove to be short-lived, as the SED quickly lost power. At its last session on 3 December 1989, the Central Committee elected Sieber to a commission tasked with analyzing the causes of the crisis in the SED and in society.^[8]