In the 1990 East German elections, he was elected to the Volkskammer (parliament of the GDR) on behalf of the Green Party.
During that time, he was a member of the German People's Council (Deutscher Volksrat) from 1948-49, and from 1950-54 a member of the Volkskammer.
He was at various times Secretary General of the VdgB (the Peasants Mutual Aid Association), deputy in the parliament (the Volkskammer) and a member of the Central Committee of the SED.
Platzeck was elected member of the Volkskammer in 1990 for the Green Party and was parliamentary secretary of the joined faction of Greens and Bündnis 90 (Alliance 90).