Platzeck co-founded ARGUS, a Potsdam environmental organization, with and at the initiative of Carola Stabe in April 1988. In April 1989, he joined the Liberal Democratic Party of Germany but left it shortly thereafter. He represented ARGUS at the founding of the "Grüne Liga" association of local environmental organizations in East Germany in November 1989. During the political "Wende" of 1989–1990 that led to German Reunification he was their speaker at the East German Round Table talks. From February to April 1990 he represented the oppositional radical Green Party as Minister without Portfolio in the last non-elected but legitimate government of the GDR. 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). In October 1990 Platzeck became a member of the Landtag of Brandenburg for Bündnis 90 (Alliance 90). He was Minister for the Environment in a coalition government with the SPD and FDP from 1990 to 1994, when the coalition broke up.