<p>Mainstream Circular Economy (CE) frameworks have systematically depoliticized material flows, privileging technical optimization and efficiency gains while marginalizing communities, imposing knowledge hierarchies, and disregarding social justice. Solidarity Circularity (SC) reconceptualizes circular transitions as contested terrains where governance structures, justice, and transformative potential are constitutive rather than peripheral to sustainability outcomes. This framework defines waste as a socially constructed, politically mediated category rooted in power relations, and not as a neutral technical problem. Drawing on commons theory, Social and Solidarity Economy, degrowth perspectives, and discard studies, a two-dimensional typology maps CE pathways along participatory governance (low-centralized to high-inclusive) and circular depth (shallow downstream to deep upstream) axes. This reveals four ideal-typical socio-material configurations, Market Circularity, Efficiency Circularity, Reformist Circularity, and Solidarity Circularity, each generating distinctive landscapes of justice, labor conditions, and value distribution. SC emerges as a transformative pathway integrating deep circularity with high participatory governance, and it is operationalized through nine principles, Grassroots Governance, Just Distribution, Labor Dignity, Knowledge Pluralism, Decommodification, Futurity Ethics, Needs-Based Metabolism, Socio-Ecological Integration, and Transformative Solidarity, each paired with indicators and practical applications. This work delivers empowering frameworks for practitioners and policymakers pursuing social and ecological justice in circular transitions.</p>