Regional governments are one of the largest but most understudied interest groups, employing a wide range of advocacy tactics like hiring professional lobbyists and face-to-face lobbying. However, we know little about why some succeed in influencing public policy while others do not. This gap arises because existing theories of interest groups and intergovernmental mobilization focus on resources—money and legitimacy—that regional governments typically lack control over. To address this, I propose a theoretical framework of intergovernmental lobbying success tailored to regional governments, emphasizing the convergence of five distinct conditions. Using new and original data on the 26 Swiss cantons’ influence on federal policy and employing set-theoretic methods (csQCA), I demonstrate that no single condition explains intergovernmental lobbying success. Instead, five causal pathways lead to a regional government shaping federal policy in line with its preferences. These findings have significant implications for understanding the effects of intergovernmental lobbying on representation, inequality, and unequal policy responsiveness, potentially contributing to rising political discontent, growing rural resentment, or citizen alienation.