Transformational leadership (TFL) has been shown to affect employees' job performance, and the literature offers a large variety of explanatory processes. Integrating the diverse literature related to the mechanisms that mediate the TFL-performance relationship, the current study identified five core mechanisms—affective, motivational, identification, social exchange, and justice enhancement—that are consistent with established social and psychological theories. Meta-analysis involving > 600 samples was conducted to test these mechanisms. General support was found for each of the five mechanisms. The findings showed that TFL was related to variables that represented these mechanisms, which in turn were associated with non-self-report measures of employees' task performance, citizenship behavior, and innovative behavior. An integrative model was further proposed and tested to show the central role of leader-member exchange in the relationships between TFL, other mediating variables, and performance outcomes. This study contributes to the literature by strengthening researchers' theoretical understanding of the major social and psychological processes by which transformational leaders promote followers' job performance.