The study examined the relationship between head teachers' leadership strategies and teacher content mastery in selected public secondary schools in Kanungu District, Uganda. Content mastery, defined as teachers' comprehensive understanding of subject matter, pedagogical content knowledge, and ability to translate curriculum into meaningful learning experiences, and was recognized as fundamental to effective teaching. The study investigated how instructional leadership, transformational leadership, and participatory leadership strategies employed by head teachers influenced teachers' depth of subject knowledge, curriculum understanding, and continuous content updating in their respective teaching areas. A correlational research design with quantitative approach was employed. The study sampled 162 teachers and 12 head teachers from 12 purposively selected public secondary schools in Kanungu District. Data were collected using two structured questionnaires: the Leadership Strategies Assessment Questionnaire (LSAQ) and the Teacher Content Mastery Scale (TCMS), both utilizing 5-point Likert scales. The LSAQ comprised 33 items measuring instructional leadership, transformational leadership, and participatory leadership dimensions. The TCMS contained 30 items assessing subject matter knowledge depth, pedagogical content knowledge, curriculum mastery, and content updating behaviors. Reliability testing yielded Cronbach's alpha coefficients of 0.89 for LSAQ and 0.86 for TCMS. Data analysis employed Pearson's correlation coefficient and multiple regression analysis using SPSS version 26. Findings revealed a significant positive relationship (r = 0.768, p < 0.01) between head teachers' leadership strategies and teacher content mastery. Among leadership dimensions, instructional leadership demonstrated the strongest correlation with content mastery (r = 0.794, p < 0.01), followed by transformational leadership (r = 0.721, p < 0.01) and participatory leadership (r = 0.678, p < 0.01). Regression analysis indicated that leadership strategies collectively explained 59.0% of variance in teacher content mastery (R² = 0.590, F = 187.63, p < 0.000). Teachers in schools where head teachers frequently conducted subject-specific supervision scored significantly higher in content mastery (M = 4.31, SD = 0.52) compared to those with minimal supervision (M = 2.94, SD = 0.81). Subject matter knowledge depth showed the highest mean score (M = 3.72, SD = 0.76) while content updating behaviors recorded the lowest (M = 3.08, SD = 0.94). The study concluded that head teachers' leadership strategies significantly influenced teacher content mastery in Kanungu District's public secondary schools. Instructional leadership emerged as the most critical factor, demonstrating that head teachers who engaged in subject-specific supervision, facilitated access to current teaching resources, promoted subject department collaboration, and created opportunities for content-focused professional development substantially enhanced teachers' mastery of subject content. The findings underscored that effective school leadership extended beyond administrative management to include active cultivation of teachers' disciplinary expertise. The Ministry of Education and Sports should establish specialized instructional leadership training programs emphasizing subject-specific supervision competencies for head teachers across all curriculum areas. District education offices should create subject-based teacher networks coordinated by head teachers to facilitate content knowledge sharing and collaborative learning. Schools should institutionalize departmental professional development sessions led by head teachers focusing on emerging content developments and pedagogical innovations. Education authorities should provide adequate budgetary allocations for subject-specific teaching resources, reference materials, and teacher access to digital content repositories. Additionally, teacher performance appraisal systems should incorporate content mastery assessment components to ensure continuous improvement in subject matter expertise.