BACKGROUND: Despite extensive efforts to tackle the unequal levels of leisure-time physical activity (LTPA) among adults, our understanding of how these inequalities are sustained over time is minimal. Existing approaches often overlook the complex dynamic, and typically nonlinear interactions, which shape physical activity patterns. Therefore, this paper aims to capture these dynamic interactions and processes which influence an individual's decision to practice LTPA, with a specific focus on the influence of income. METHODS: The conceptual model was developed in 4 main stages: (1) initial draft development, (2) realist reviews, (3) expert consultation, and (4) finalization. RESULTS: The conceptual model has intention as its central construct to practice LTPA, and intention is directly influenced by dynamic interrelated processes between individual's economic, psychosocial, and perceived physical environment factors. CONCLUSION: From the multiple theories, evidence, and expert agreement, we are confident that our conceptual model expresses the dynamic interactions which shape an individual's decision to practice LTPA in a context of socioeconomic inequalities. Going forward, this work will be used to conceptualize and inform the development of an agent-based model to simulate LTPA inequalities among adults and can be expanded or adapted to other uses, such as intervention development.