After the end of World War II, Reimann was a candidate of the Western KPD organization for the executive committee of the Sozialistische Einheitspartei Deutschlands (SED) but had to quit as the SED activities were limited to East Germany.
He joined the Free German Youth in 1951 and the Socialist Unity Party of Germany (Sozialistische Einheitspartei Deutschlands, SED) in 1955.