Citizen participation in policy decision-making is vital for ensuring transparency, accountability, and responsiveness in governance. This systematic literature review examines the relationship between citizen participation and policy legitimacy, exploring various factors influencing citizen involvement in decision-making processes. The analysis reveals a positive correlation between the level of citizen participation and the legitimacy of policies. Indicators such as public perception of fairness, support and acceptance, compliance with policy, trust in government institutions, perceived effectiveness of policies, transparency, and accountability contribute to policy legitimacy. Moreover, demographic, institutional, psychological, technological, and cultural factors play significant roles in shaping citizen participation. The findings underscore the importance of inclusive and effective citizen engagement in enhancing policy legitimacy, strengthening democracy, and fostering responsive governance.