City engagement in transnational municipal networks in the migration field (TMNs) is widely seen as positive. Yet, the evidence for that optimism is limited and analysis of the functions and outcomes of these networks leaves many questions unanswered. This article presents a case study of the City Initiative on Migrants with Irregular Status in Europe (C‐MISE) as a contribution to our understanding. On the basis of documentary evidence and interviews with participants, it explores the operation of a network in a sensitive policy field. It throws light on the network's instrumental and “symbolic” functions and the relationship between them; on the factors which shape its operation and facilitate the accommodation of difference through internal socialization; and on the significance of the outcomes for the future governance of migration by urban and higher tiers. Conceptually, deconstructing “symbolic” functions into those of legitimation, substantiation and framing, facilitates a nuanced analysis of the role that each plays and exploration of a tension where those roles bordered on advocacy for policy change. In a critical assessment of the network's outcomes, it finds grounds for cautious optimism on the role TMNs can play in reframing debates, in the urban governance of migration, and in shifting its overall management from below.