The purpose of this study was to investigate on The Influence of Principals‟ Instructional Supervision Roles on Students‟ academic performance in public secondary schools in Shinyanga Municipal. A mixed research approach was employed with convergent parallel design specifically cross sectional survey and phenomenological design. A total of 155 participants were selected. The findings established that instructional supervision was influenced by principals for increasing student academic performance. Principals monitoring of students‟ academic improvement and visiting classrooms for lesson observation scored very highly as roles frequently performed. The study recommends that instructional supervision should influence in public secondary schools for improving students‟ academic performance. The study further suggests that instructional supervision should be carried out regularly by principals in order to improve students‟ academic performance. Principals should carry out effective supervision by providing feedback to supervisee (teachers); this helps supervisee identify area of weakness to make improvements and teach effectively. Also the government of Tanzania should provide enough teaching and learning materials, good infrastructure like teachers‟ office, libraries and classes in public secondary schools so as to help principals‟ carry- out supervision regularly. Further research studies should be carried out to the effectiveness of Principals‟ Instructional Supervision on Students‟ academic performance in private secondary schools, an investigation on the effectiveness of government education quality assurance departments in ensuring principals‟ instructional supervision in secondary schools as well as factors influencing majority male students‟ enrollment in secondary over female as observed in the study.