This study investigates the influence of citizen participation on effective policy implementation in local government administration in Nigeria. It specifically examines the effects of community involvement in decision-making, public accountability, transparency in local government administration, and citizens' participation in project monitoring and evaluation on policy implementation at the grassroots level. The research is motivated by persistent implementation challenges associated with weak citizen engagement, inadequate accountability, and limited transparency within the Nigerian local government system. A descriptive survey research design was employed, with data collected through a structured questionnaire administered to selected respondents. The instrument was validated by experts, and its reliability was established using Cronbach's Alpha. Data analysis involved descriptive statistics and Multiple Regression Analysis at the 0.05 level of significance. The study is anchored on Participatory Democratic Theory and Stakeholder Theory, both of which emphasize inclusive governance and collaborative decision-making. Findings indicate that active citizen participation is essential for improving policy implementation, strengthening accountability, promoting transparency, and enhancing public confidence in local government administration. The study recommends institutionalizing participatory governance through regular stakeholder engagement, transparent administrative practices, effective accountability mechanisms, and active citizen involvement in monitoring and evaluating public programmes. This research contributes to the literature on participatory governance and offers practical policy directions for strengthening grassroots governance and sustainable development in Nigeria.