Although self-control is commonly believed to contribute to greater well-being, current evidence is inconclusive due to methodological and statistical issues. Indeed, there are both theoretical and empirical grounds to expect the opposite causal relation: wellbeing could precede self-control. We aimed to clarify this debate with two three-wave longitudinal studies, one on an Asian and the other on an American sample. We applied the random intercept cross-lagged panel model (RI-CLPM) to disentangle the stable-trait-level associations and within-persons relations between self-control and well-being. We found that earlier levels of well-being positively predicted levels of self-control 1 month (Study 2) and 6 months (Study 1) later. However, self-control did not predict later well-being. Our findings emphasize the need to reconsider the interpretations of previous—mostly between-persons—findings about self-control and well-being. Implications for understanding trait self-control, alternative causal models between self-control and well-being, and the primacy of well-being are discussed.