The purpose of this paper is to examine whether corporate governance has a mediating or moderating effect on the relationship between capital structure and firm performance. This study employs a quantitative method with a sample of 224 Italian non-financial listed firms from 2013-2017. Collected data were analysed using OLSand GMMestimations to test the research hypotheses and to assess the mediating and/or moderating effect of corporate governance. Based on an integrated theoretical framework that draws insights from agency theory, pecking order theory, and trade-off theory, our results are threefold. First, we find that capital structure has a negative and significant impact on firm performance. Second, we show a significant association between corporate governance mechanisms and firm performance. Specifically, we find that board size has a negative effect on firm performance, while board independence and managerial ownership has a positive effect on firm performance. Finally, our results indicate that corporate governance mechanisms do not mediate, but instead moderate the association between capital structure and firm performance. This study further suggests some important policy implications for both theory and practice.