A rich tradition in self-control research has documented the negative consequences of exerting self-control in one task for self-control performance in subsequent tasks. However, there is a dearth of research examining what happens when people exert self-control in multiple domains simultaneously. The current research aims to fill this gap. We integrate predictions from the most prominent models of self-control with recent neuropsychological insights in the human inhibition system to generate the novel hypothesis that exerting effortful self-control in one task can simultaneously improve self-control in completely unrelated domains. An internal meta-analysis on all 18 studies we conducted shows that exerting self-control in one domain (i.e., controlling attention, food consumption, emotions or thoughts) simultaneously improves self-control in a range of other domains, as demonstrated by, for example, reduced unhealthy food consumption, better Stroop task performance, and less impulsive decision making. A subset of nine studies demonstrates the crucial nature of task timing -when the same tasks are executed sequentially, our results suggest the emergence of an ego depletion effect. We provide conservative estimates of the self-control facilitation (d = |0.22|) as well as the ego depletion effect size (d = |0.17|) free of data selection and publication biases. These results (i) shed new light on self-control theories, (ii) confirm recent claims that previous estimates of the ego depletion effect size were inflated due to publication bias, and (iii) provide a blueprint for how to handle the power issues and associated file drawer problems commonly encountered in multi-study research projects.