Last two decades, corporate accounting scandals have represented a serious challenge to economic sustainability. To protect the shareholders right against abusive managerial conduct, the concepts of corporate governance structures and provisions have widely attracted the attention of practitioners and researchers. The main purpose of this paper is to examine the linkage between corporate governance and the performance of non-financial firms listed on Muscat Securities Market over the period 2007-2017. Additionally, whether financial leverage acts as a mediating factor is investigated. A panel fixed effect regression is conducted to test if there is a relationship between corporate governance, capital structure and firm performance. Overall results show that women on board, audit committee size, leverage and firm size are positively related to firm performance. The study presents a strong understanding to senior management to be focused more on corporate governance codes and regulations, as well as to both internal and external auditors to strictly monitor the application of corporate governance regulations.