Performance Management System (PMS) is a critical tool for monitoring and evaluating employee performance against organizational objectives in both public and private sectors. Despite its adoption, limited research exists on its direct impact on organizational effectiveness. This study investigated the influence of PMS on organizational effectiveness at the Teachers Service Commission (TSC), focusing on performance planning, monitoring, rating, and development. The study was guided by goal-setting theory, expectancy theory, and learning curve theory. A descriptive research design was employed, targeting 375 Secretariat Staff at TSC Headquarters. Using stratified random sampling, 30% of the population was selected, yielding a sample size of 113. Data was collected through questionnaires whose reliability and validity were confirmed. Analysis was conducted using SPSS version 22, applying descriptive statistics (percentages, means, and standard deviations) and inferential statistics (correlation and multiple regression). Findings revealed that performance planning (r=0.506, β=0.225, p<0.05), performance monitoring (r=0.831, β=0.136, p<0.05), performance rating (r=0.961, β=0.431, p<0.05), and performance development (r=0.693, β=0.105, p<0.05) all had positive and statistically significant effects on organizational effectiveness. Among these, performance rating emerged as the strongest predictor; while monitoring and planning were vital for accountability and goal alignment. Continuous employee development was also found essential for capacity building and sustaining long-term improvements. The study concludes that PMS significantly enhances organizational effectiveness at TSC and recommends further research across institutions. Policymakers should strengthen fairness, transparency, and resource allocation, while continuous training, mentoring, and integration of PMS principles in teacher preparation programs are vital for professional and institutional growth.