Background: For more than 30 years, drug consumption rooms (DCRs) have been implemented in Western countries. DCRs are supported by a large body of evidence about public safety and public health effectiveness. However, a political consensus has never been achieved in Belgium on amending the existing law that explicitly penalises the supply of a room for facilitating drug use. Despite this adverse legal and policy framework, a DCR opened in the city of Liège in 2018. In this case report, we applied the theoretical framework proposed by Shiffman and Smith for policy agenda setting, in order to describe and assess how political and legal barriers were overcome in the process of opening the DCR. Case presentation: For some years, fieldworkers and some city policymakers argued for DCR implementation in Belgium, but without gaining the support of the national authorities, mainly for ideological reasons. In order to address this debate, a feasibility study of DCR implementation in Belgian cities was commissioned. At the national level, an institutional debate took place about the political responsibility for DCRs as a public health intervention, as health care is mainly a matter of regional policy. The lack of consensus led to a situation of political deadlock. Meanwhile, the publication of the study report and the context of local elections offered an opportunity for Liège authorities to reignite the local debate on DCRs. At the local level, law enforcement, care professionals, residents, users, and the press were all involved in the implementation process. Therefore, a local consensus was formed and despite the absence of any national legal change, the DCR opened 1 month before the local elections. It has been working without major medical or legal incident since then. Incidentally, the mayor of Liège was re-elected. Conclusions: Although the lack of a legal framework may engender instability and affect longer-term effectiveness, the DCR implementation in Liège was successful and was based on a local consensus and ...