This study examined Principals’ Leadership Effectiveness and Management of Public Secondary Schools in Cross River State, Nigeria. The purpose of the study was to investigate influence of principals’ leadership effectiveness in the areas of instructional supervision, communication, and provision of instructional materials on the management of public secondary schools. Three research questions guided the study and three null hypotheses were formulated and tested. The review of literature was done under theoretical framework, conceptual framework and empirical studies. The study adopted survey research design. The population of the study comprised 12,930 principals and teachers from the 293 public secondary schools in the state. A sample of 1737 principals and teachers were taken for the questionnaire using multi-stage sampling technique of Principals’ Leadership Questionnaire (PLEQ) with reliability coefficient of 0.97. Mean and standard deviation were used to answer the research questions. Chi-Square test was used to test the hypotheses at 0.05 level of significance. The result showed that principals’ leadership effectiveness do significantly impact on management of secondary schools in the areas of instructional supervision, communication, and provision of instructional materials in the management. Based on the findings of the study, it was recommended among others that principals should be adequately enlightened with more robust supervision strategies through seminars and conferences which may include classroom observation, analysis/strategy, post observation conferences and post conferences analysis and that Ministries of Education should make it mandatory for all school heads to be involved in students’ evaluation in order to assess teachers’ job outputs as well as students’ academic performance.