Abstarct: Product market competition is one of the most influential external forces shaping managerial behavior and can significantly affect the time horizon of strategic decision-making. However, the moderating role of corporate governance mechanisms in this relationship, particularly in emerging markets, has not yet been fully explored. Accordingly, this study investigates the effect of product market competition on managerial decision-making horizon and examines the moderating role of corporate governance in this relationship among firms listed on the Tehran Stock Exchange. The empirical findings reveal that product market competition has a positive and statistically significant effect on managerial decision-making horizon. This finding suggests that greater competitive pressure encourages managers to undertake higher levels of capital investment and adopt a longer-term strategic perspective. The results also indicate that corporate governance has a negative and statistically significant effect on managerial decision-making horizon, highlighting the disciplinary and monitoring role of governance mechanisms in constraining long-term investments and increasing managerial attention to the efficiency of resource allocation. Furthermore, the interaction effect between product market competition and corporate governance is negative and statistically significant, indicating that corporate governance weakens the positive effect of product market competition on managerial decision-making horizon. In other words, although competitive market conditions motivate managers to pursue long-term strategic investments, effective corporate governance mechanisms ensure that such investments are subject to rigorous monitoring, thereby preventing excessive or economically unjustified investments and promoting more efficient investment decisions.