Although cognitive ability and conscientiousness have been found to predict work-related performance, less is known about whether and when certain mediating variables help explain these relationships. This study examined meta-analytically whether self-efficacy mediates the cognitive ability-performance and conscientiousness-performance relationships, and whether task complexity moderates the extent to which self-efficacy mediates these relationships. Results indicated that cognitive ability and conscientiousness positively relate to self-efficacy, but that the magnitude of these relationships varies with task complexity. Furthermore, results showed that self-efficacy mediates the relationships of cognitive ability and conscientiousness with performance on simple tasks, but not on complex tasks. Implications and directions for future research are discussed.