Altvater supported the German Greens for some time, but after the 1999 military intervention in Kosovo (which as a member of the governing coalition the party had to support) increasingly maintained a critical distance. He was a member of the Bundestag Commission of Inquiry "The World Economy - Challenges and Answers (1999–2002)". Altvater was a supporter of ATTAC (he was a member of its Scientific Advisory Board) and the World Social Forum.