In the federal elections of 2013 and 2017, Janecek was the Green Party candidate of the Munich constituency 221 München-West/Mitte. Both times he received his seat in the Bundestag through his position on the Green electoral list. In parliament, Janecek is member of the Committee on Economic Affairs and Energy as well as of the Committee on the Digital Agenda. Between 2013 and 2017, he also served as his parliamentary group's spokesperson on economic policy. Since 2018, he has been the group’s spokesperson on the digital economy., since October 2019 he has also been the group's spokesperson on industrial policy. Janecek also serves as a member of the Study Commission of the Bundestag on "Artificial Intelligence – Social Responsibility and Economic, Social and Ecological Potential".