The role of the school principal is to provide a school environment that promotes academic achievement. The purpose of this study was to investigate the relationship between principals’ human resource management practices and academic achievement in public secondary schools. Embedded mixed method research design was adopted for the study. The target population comprised principals, deputy principals and heads of department drawn from Bungoma East Sub-County in western Kenya. In a total of 33 schools, 33 principals and 33 deputy principals were automatically included in the study while 114 heads of department were selected through random sampling as respondents for the study. Data was collected using interview schedule administered to the principals while questionnaires were administered to deputy principals and heads of department. Data on academic achievement was collected using document analysis. A pilot study was done in three schools before the main study to establish validity and reliability of the research tools. A correlation test was done between the principals’ human resource management practices and academic achievement in public secondary schools. A strong positive relationship was found between the principals’ human resource management practices and academic achievement in public secondary schools. It was thus concluded principals’ human resource management practices affect students’ academic performance. The study recommends that school principals should employ effective human resource management practices such as competitive recruitment, professional development of staff, rewarding and staff welfare programmes.