[1][2] After completing elementary school, Grüneberg learned the trade of a bricklayer (1936–1939) and worked in this field until his conscription into the Kriegsmarine in the spring of 1941.

After the war, he was captured by the British and released in August 1945, after which he worked as a bricklayer in Oldenburg, Lower Saxony.

On 1 March 1946, he joined the KPD, which merged with the SPD later that year to form the Socialist Unity Party of Germany (SED).

Alongside his work, he completed a distance-learning program at the "Karl Marx" Party Academy, earning a diploma in social sciences.

He became the secretary of the SED Central Committee for State and Legal Affairs[3] and concurrently became a member of the Volkskammer,[1] nominally representing a constituency in southwestern Bezirk Potsdam.

This was particularly evident under the leadership of Erich Honecker, under whom Grüneberg expanded his power after falling out of favor with Walter Ulbricht in 1969 due to 'exaggerations.'

This led to internal criticism of Grüneberg – notably by the Central Committee Secretary for Economics, Günter Mittag.

Grüneberg, together with his ally Bruno Kiesler (Head of the Agriculture Department of the Central Committee), attempted to alleviate the consequences through increased cooperation, which yielded limited success.