Subnational entities in federal states typically retain a degree of sovereignty and enjoy leeway in implementation, raising questions such as whether—and how—international law is actually implemented at the subnational level. This article sheds light on these questions, using two contrasted case studies in Switzerland: The Istanbul Convention on domestic violence and the European Union (EU) Directive 2016/680 on data protection. Based on a document analysis of the law‐making process and 44 semi‐structured interviews with national and subnational political actors, we observe how international obligations are legally implemented, that is, transposed into legislation at the subnational level. Our results show that: (1) Subnational civil servants play a decisive role, while members of parliament are marginal. (2) Civil servants may constitute Vertical Epistemic Communities (VECs), which are able to “technicize” the issue to ensure swift implementation through administrative venues. (3) VECs are particularly influential as they use intercantonal conferences as institutional platforms to shape implementation processes. Otherwise, implementation becomes politicized, and its success strongly depends on subnational politics.