Scholars have paid extensive attention to transformational leadership for decades. However, existing studies still lack ample discussions on the underlying mechanism and boundary conditions of its influence on employee job satisfaction. This study proposed a moderated mediation model based on social exchange theory. We collected survey data from 211 frontline employees to verify our hypotheses. The results showed that transformational leadership was positively associated with employee job satisfaction via the mediation role of the perceived employee relations climate. Furthermore, the relationship between transformational leadership and the employee relations climate, as well as the indirect relationship between the two, was demonstrated to be more significant for male employees. This study offered a new account of the mechanisms of transformational leadership and clarified a boundary condition for its effectiveness.