This article analyses cause lawyering as a critical form of resistance to uneven European Union (EU) mobility regimes. Grounded in the proclamation of a migration crisis during 2020–21 in the Canary Islands, Spain, when newly arrived racialized migrants in irregular situations faced different types of (im)mobilization during their transits to continental Europe, the article shows that cause lawyering is a significant strategy for disputing exclusionary dimensions of law and policy, and/or (im)mobility regulations when rules are arbitrarily applied or violated. The case is illustrated ethnographically and follows various expert lawyers in migration working within formal or informal structures, as well as non-lawyer allies such as ombudsmen, activists, friends, or migrant families, who facilitate the navigation of migrant mobilities using human rights and national and international laws and regulations. The analysis focuses on their actions in practice and shows how they challenge specific mobility rules within the EU’s mobility regimes, create procedures to deal with bureaucracies and problems regarding access to legal services, and strategically litigate individual cases in local, national and supranational jurisdictions. By drawing attention to the plurality of actors performing mobility-related cause lawyering to challenge uneven regimes of (im)mobility, the article contributes to the critical work that analyses practices of migrant resistance by going beyond the portrayals of unauthorized migrants battling alone against the odds as victims or heroes.