This study examined the relationship between teacher competence in competence-based curriculum (CBC) implementation and students' academic achievement in government secondary schools in Rubanda District, Uganda. Following Uganda's adoption of the competence-based lower secondary curriculum, the quality of implementation— and hence learner achievement—depends heavily on teachers' capacity to deliver learner-centred, competence- oriented instruction. The study investigated how pedagogical competence, assessment competence, content mastery, and ICT and resource competence relate to students' academic achievement. A cross-sectional survey design with a mixed-methods approach was adopted, and data were collected from 190 respondents comprising teachers, head teachers, and students using structured questionnaires, lesson observation, and interviews. Descriptive statistics, Pearson correlation, and regression-based path analysis were used. The results revealed a strong positive and significant relationship between teacher competence and academic achievement (r = 0.66, p < 0.01), with the competence dimensions jointly explaining 63.0% of the variance in achievement (R² = 0.630). Pedagogical competence and assessment competence emerged as the strongest predictors. The study concludes that teacher competence in CBC implementation significantly enhances academic achievement and recommends targeted in- service training in learner-centred pedagogy and competence-based assessment.