This study examined the influence of school leadership on academic performance in government secondary schools in Mbarara District, Uganda. Recognising that the head teacher's leadership is a pivotal determinant of school effectiveness, the study investigated how instructional leadership, participative decision-making, supervision and monitoring, and resource management relate to students' academic performance. A descriptive cross-sectional design with a mixed-methods approach was used, and data were gathered from 180 respondents comprising head teachers, teachers, and members of school management committees through questionnaires and interviews. Descriptive statistics, Pearson correlation, and multiple regression were employed for analysis. The results showed a strong positive and significant relationship between school leadership and academic performance (r = 0.65, p < 0.01), with leadership dimensions jointly accounting for 50.7% of the variance in performance (R² = 0.507). Instructional leadership and supervision emerged as the strongest predictors. The study concludes that effective school leadership is central to improving academic performance and recommends strengthening the instructional and supervisory capacity of head teachers.