Social movements play a crucial role in shaping legislative outcomes, yet the mechanisms through which movement characteristics influence federal lawmaking remain insufficiently explored. This study examines how social movement size and organizational diversity affect the process and substance of federal legislation. Drawing on theories of political mobilization, resource mobilization, and institutional access, the paper argues that larger movements enhance legislative visibility and agenda-setting capacity, while greater organizational diversity strengthens policy influence by enabling strategic specialization, coalition-building, and sustained engagement with state institutions. Using a mixed-method approach that combines quantitative analysis of legislative outcomes with qualitative case studies of selected federal laws, the study demonstrates that movements characterized by both substantial membership and heterogeneous organizational structures are more likely to achieve favorable legal outcomes. The findings reveal that organizational diversity mitigates internal coordination challenges often associated with large movements, transforming numerical strength into effective legislative leverage. This research contributes to socio-legal scholarship by offering a nuanced framework for understanding how internal movement dynamics shape federal lawmaking and provides practical insights for policymakers and activists seeking to enhance democratic participation in legislative processes