The study investigated the combined effects of ownership structure, board effectiveness and managerial discretion on firm performance using agency theory as an analytical framework. Measures of performance used in the study were Return on Assets, Return on Equity and Dividend Yield. Using Pearson''s Product Moment Correlation and Logistic Regression, Step-wise regression and ANOVA to analyze data obtained from companies listed at the Nairobi Stock Exchange, the study found out that Ownership Concentration and Government Ownership have significant negative relationships with firm performance. On the other hand, Foreign Ownership, Diffuse Ownership, Corporation Ownership, and Manager Ownership were found to have significant positive relationships with firm performance. The results of this study have indicted the Board of Directors for not playing any meaningful role in corporate governance in Kenya. On the other hand, the results support the need for managers to bear more responsibility of their mismanagement and also share in the residual income of the firms they manage.