Mindfulness and character strengths significantly contribute to psychological wellbeing in various contexts. Empirical studies further imply that mindfulness-based interventions can cultivate a wide range of strengths, which in turn facilitate the wellbeing of individuals. However, no study has examined this hypothesis. The current study underpins this argument with empirical pieces of evidence from cross-sectional (Study 1) and longitudinal (Study 2) data by investigating the relationship between character strengths, mindfulness, and psychological wellbeing among community (n = 375) and undergraduate populations (n = 229). Five Facet Mindfulness Questionnaire, Brief Strengths Scale, and Flourishing Scale were administrated. As hypothesized, the results of the cross-sectional investigation confirm that mindfulness and character strengths are conceptually related constructs with significant contributions to psychological wellbeing. Temperance Strength and Interpersonal Strength further mediate the relationship between Observing facet of mindfulness and Flourishing. Furthermore, investigating the relationship among mindfulness, strengths, and psychological wellbeing using Longitudinal Mediation Modeling reveals a clear picture. After the baseline of the outcomes is controlled, the 6-month longitudinal study indicates that the past level of Observing facet of mindfulness can predict the present level of Temperance Strength, which in turn predicts future Flourishing. These results highlight the importance of Observing facet in mindfulness and Temperance Strength, which provide another possible explanation on how and why mindfulness can affect psychological wellbeing among general populations. Future Strength-based Mindfulness Intervention Programs can be developed based on these findings.