Historian; studied history, Eastern European studies and law, first at the University of Bremen, later in Hamburg. Member of Bündnis 90/Die Grünen Hamburg since 1998; deputy state chairman from 2011 to 2015. Member of the Bundestag from 2008 to 2021.

Board member of Europäische Bewegung Deutschland e.V. from 2014 to 2018. Vice-President of Europäische Bewegung Deutschland e.V. since 2018. Chairman of the Polish-German Parliamentary Group in the Bundestag from 2018 to 2021.

Chairman of Südosteuropa Gesellschaft since February 2020. Federal Government Special Envoy for the Western Balkans since 1 March 2022.