Abstract: This study delves into the intricate interplay between managers’ overconfidence, varying degrees of managerial discretion, and corporate investment efficiency within the context of global economic transformation and a progressively complex market environment. Drawing on a comprehensive dataset spanning 2010 to 2019 from Chinese A-share listed companies on the Shanghai and Shenzhen stock exchanges, our research sheds light on several pivotal findings. Firstly, the study underscores the detrimental impact of managers’ overconfidence on corporate investment efficiency, manifesting as either overinvestment or underinvestment. This finding underscores the crucial role of psychological traits in shaping corporate decision-making processes, challenging the assumption of complete rationality often assumed in traditional economic models. Specifically, the research reveals that overconfident managers tend to overestimate their abilities and project success rates, leading to distorted investment decisions. Secondly, we uncover significant variations in the negative consequences of managerial overconfidence across different types of managerial discretion environments. In settings characterized by high external environmental discretion, notably in resource-rich market conditions, the adverse effects of overconfidence are mitigated in overinvested firms. Conversely, in firms exhibiting underinvestment, the moderating effect of the market environment remains insignificant. This observation underscores the mitigating influence of a favorable market environment on the decision-making biases of overconfident managers. On the other hand, when internal organizational discretion is constrained, the overall negative impact of managerial overconfidence diminishes, highlighting the constraining effects of organizational structures and internal norms on managerial behavior. Notably, special situational discretion, such as enterprise ownership and regional institutional environments, fails to exhibit a pronounced moderating effect, potentially attributed to the intricate interplay of multiple factors and the increasing convergence of market conditions. Thirdly, our analysis underscores the pivotal mediating role of risk-taking behavior in the relationship between managerial overconfidence and investment efficiency. Overconfident managers, driven by their inflated self-assurance, tend to undertake higher levels of risk in pursuit of greater returns. This enhanced risk-taking, while potentially fostering innovation and competitiveness, can also lead to suboptimal investment decisions and a subsequent decline in investment efficiency. Our empirical results robustly support the transmission mechanism of “overconfidence - risk-taking - corporate investment efficiency,” elucidating the indirect pathways through which psychological biases manifest in corporate financial outcomes. Collectively, this study contributes to the growing body of literature examining the intricate relationship between managers’ psychological traits and corporate investment behaviors. By integrating managerial discretion as a critical moderating factor, our research offers novel insights into how firms can optimize their investment decisions amidst a complex and dynamic economic landscape. Practical implications include emphasizing the importance of assessing managerial psychological profiles during the hiring process, integrating psychological trait development into training programs, and establishing robust decision-making, evaluation, and monitoring mechanisms to mitigate the risks associated with managerial biases. Furthermore, our findings underscore the significance of tailoring managerial discretion frameworks to balance creativity and risk management, ultimately facilitating high-quality economic development and corporate sustainability.