In 2018, cities from Africa, Europe, North, and South America officially submitted input to the state-led negotiations of the Global Compact for Migration. In the same year, the Mayors Mechanism was established within the Global Forum on Migration and Development, and in 2019, cities made pledges to localize the Global Compact on Refugees. At first sight, this engagement seems surprising, given that migration and displacement are mostly areas of national decision making. How, then, did it become possible for cities to claim a role in global migration governance? And how do cities attempt to play this role? While cities as integration actors have received growing academic attention, it is time to focus on city agency in global migration governance. To explore this phenomenon, this article introduces role theory to research on city diplomacy in migration studies. The analysis shows that the combination of the glocalized representation of migration challenges (linking the local and global levels), the glocal role claimed by cities, and the passive role attributed to nation-states can empower cities to demand an active role in global migration governance. Cities draw on this role to promote three forms of city diplomacy as adequate and feasible actions on the global stage: advocating for rights-based migration policies; striving to gain access to international funding and cooperation partners; and demanding a seat at intergovernmental negotiation tables. In closing, the article reflects on the risks and constraints of city diplomacy in global migration governance and shows directions for future research.