Cities worldwide develop a variety of urban policies that address the precarious situation of irregular migrants. By doing so, cities intervene in a policy-making realm that is commonly perceived as the prerogative of national states and they thereby challenge the national state as the only regulatory body over immigration and citizenship. We compare policy-making in support of irregular migrants in the two biggest Swiss cities of Geneva and Zürich. Whereas Genevan authorities and local societal actors established a successful regularisation programme (called Operation Papyrus), actors in Zürich aim to create an urban ID card programme (called Züri City Card). We find that the institutional setting of the two cities (as a city-state or as a city in a state), the presence or absence of multilevel governance networks as well as societal actors’ different venue shopping strategies are key for explaining these different urban policy-making processes. Cities formulate place-based urban policy responses, but these specific urban policies can be viewed within the global struggles to improve the precarious situations of irregular migrants and to fight exclusionary national politics. In essence, this article documents and explains how cities contest national state sovereignty over immigration and citizenship and it thereby calls for an urbanisation of migration theory and practice.