From 1965 to 1967 his political activism got him into trouble with the Czechoslovak communist regime, and he was arrested several times. After the suppression of the Prague Spring in 1968, he fled from Czechoslovakia and settled in West Germany. There he worked in industry and for a trade union magazine. From 1976 to 1981 he studied political science in Frankfurt, and in 1979 was involved in the establishment of Die Grünen. In the 1980s he was active in Hesse for the party, was a municipal councillor in Frankfurt 1981–1983, and was elected to the Bundestag in 1983, serving until 1985, as a member of its Foreign Affairs Committee. His main interests there were foreign affairs and security, Central and Eastern Europe and human rights. From 1985 to 1990, he was a group specialist on foreign and security policy, human rights and Eastern Europe.
Besides his political work, Horáček engaged in Czechoslovakian exile activities. He was publisher of the Czech exile magazine Listy ("Sheets"). In 1990 his Czech citizenship was restored and president Václav Havel appointed him to the Council of Advisers. He was director of the Heinrich Böll Foundation's office in Prague from 1991 to 2004, and also worked at its Bonn office 1998–2000.
