There is conceptual overlap between mental toughness and resilience, self-efficacy, and grit, although few studies have empirically examined the overlap between them. In addition, little research has examined the extent to which there is an empirical advantage of using the mental toughness framework to predict outcomes of interest. The current study therefore explored the predictive validity of mental toughness, specifically in terms of the extent to which it predicts happiness over and above the cognate constructs of resilience, self-efficacy, and grit. Three hundred and sixty-seven participants completed measures of mental toughness, resilience, self-efficacy, grit, and happiness. The correlations between the variables were explored, and a hierarchical regression analysis was conducted to examine the extent to which mental toughness predicted happiness over and above resilience, self-efficacy, and grit. There were significant correlations between mental toughness, resilience, self-efficacy, and grit. When resilience, self-efficacy and grit were entered into the regression each of them was a significant predictor of happiness, but when mental toughness was added they were no longer significant predictors, with the commitment, control of emotion, control of life, confidence in abilities, and interpersonal confidence components of mental toughness being significant predictors. Therefore, despite conceptual overlap, if the aim of research or practice is to identify individuals at risk of poor wellbeing, then this aim is better met when using the construct of mental toughness. The role of mental toughness in happiness also suggests value in examining the impact of mental toughness interventions in the domain of wellbeing.