Common prosperity constitutes an essential requirement of socialism with Chinese characteristics and a crucial manifestation of social fairness and justice. As articulated in the report to the 20th National Congress of the Communist Party of China, “We must work hard to increase the share of residents’ income in the distribution of national income and raise the proportion of labor remuneration in primary distribution.” As the main vehicle for primary distribution, enterprises are influenced by the short-term profit-seeking nature of capital and the unequal balance of power between labor and capital. Consequently, capital returns and labor remuneration struggle to achieve a balanced alignment, which in turn exacerbates the pay differentiation between management and ordinary employees and widens the internal pay gap within firms. Therefore, optimizing enterprise employment systems and mitigating unreasonable pay gaps are crucial mechanisms for ensuring that all people share in the fruits of economic development and for realizing common prosperity. The concept of “patient capital” has been mentioned repeatedly in central government policy documents. As a cornerstone of the evolving investment paradigm, patient capital investment embodies the complexity and significant potential of long-term investing. It effectively curbs the financial short-sightedness of chasing “quick profits,” promotes long-term strategic guidance for enterprises, and enhances the efficiency of resource allocation within firms. Furthermore, as a form of strategic capital, the injection of patient capital not only provides enterprises with stable financial support but also helps them optimize their capital governance structures and business models. This deep level of capital involvement enables enterprises to place greater emphasis on social responsibility during their development, thereby effectively advancing social progress and the comprehensive development of individuals. This study uses data from A-share listed companies from 2011 to 2024 as the research sample to empirically test the proposed theoretical model. All financial data are drawn from the CSMAR database. To ensure the robustness of the conclusions, this study conducts multiple tests, including variable substitution, exclusion of exogenous shocks and fixed effects, PSM, Heckman two-stage regression, and instrumental variable estimation. The baseline regression results remain valid. Empirical findings indicate that patient capital investment significantly reduces internal pay gaps within firms. Mechanism analysis reveals that patient capital investment reduces internal pay gaps through four channels: implementing long-term development strategies, improving internal governance, restraining managerial self-interested behavior, and optimizing human capital structures. Heterogeneity analysis suggests that the mitigating effect of patient capital investment on internal pay gaps is more pronounced among firms characterized by low operating profits, high levels of social responsibility, and intense market competition. This study expands the research on the microeconomic effects of patient capital investment by examining internal pay gaps within firms, providing empirical evidence of the mitigating effect of patient capital on internal pay disparities. Furthermore, by examining the roles of improving internal governance, developing long-term strategies, and optimizing human capital structures, this study reveals the mechanisms through which patient capital investment mitigates internal pay gaps, offering insights for fostering and expanding patient capital and ensuring equitable internal income distribution within firms.