This study examined the relationship among principals’ leadership behaviours, teachers’ continuing professional development, and students’ academic performance in public senior secondary schools in South-South Nigeria. A correlational survey and ex-post facto research design were adopted for the study. From a population of 84,841 teachers in 709 public senior secondary schools, a sample of 382 teachers and 71 schools was drawn from Edo and Delta States using a multistage sampling technique. Data were collected using three instruments: the Principals’ Leadership Behaviour Questionnaire (PLBQ), the Teachers’ Continuing Professional Development Questionnaire (TCPDQ), and the Students’ Academic Performance Proforma (SAPP). The reliability of the PLBQ and TCPDQ was established using the split-half method and Pearson product moment correlation, yielding coefficients of 0.82 and 0.84 respectively. Data were analysed using descriptive statistics (mean and standard deviation) and inferential statistics (linear and multiple regression) at the 0.05 level of significance. The findings revealed that principals predominantly exhibited taskcentred, people-centred, transformational, and transactional leadership behaviours, while teachers demonstrated a high level of engagement in continuing professional development activities. Students’ academic performance, as measured by SSCE results from 2013 to 2022, was generally very good. The study further established a significant relationship among principals’ leadership behaviours, teachers’ continuing professional development, and students’ academic performance. It was concluded that effective school leadership and sustained professional development practices are critical to improving academic outcomes in public senior secondary schools. Consequently, the study recommends that principals should consistently adopt leadership behaviours that promote teachers’ professional growth and enhance students’ academic achievement in South-South Nigeria.