Background: In recent years, mentalizing - the capacity to understand one's own and others' intentional mental states in social contexts - has been considered to be a protective capacity that enables adaptive processing of stress-related emotional arousal, benefits general well-being and underpins adaptive emotion regulation. Objective: Several studies using cross-sectional research designs have demonstrated the potential health-promoting effect of mentalizing in non-clinical samples. However, longitudinal evidence is scarce. The present study aimed to investigate whether mentalizing predicts well-being and emotion regulation strategies in a non-clinical sample of mainly young adults using a prospective longitudinal design. Methods: In a prospective research design, 135 participants completed questionnaires assessing well-being, psychological symptom severity and mentalizing capacity at baseline (T1). Twelve months later (T2), emotion regulation strategies (suppression and cognitive reappraisal), well-being and psychological symptom severity were assessed by self-report. The data were analyzed using multivariate linear regression analysis. Results: Impairments in mentalizing were a significant negative predictor of well-being 12months later. Furthermore, impairments in mentalizing positively predicted suppression of emotional states at T2. No association was found between deficits in mentalizing and cognitive reappraisal of emotional states over the course of 1year. Conclusion: The findings indicate that mentalizing is longitudinally associated with mental health indicators in a non-clinical adult sample. Specifically, ineffective mentalizing was associated with impaired psychological well-being and a tendency to suppress intense emotional states over a period of 1year. Future research should replicate these findings using multiple measurement timepoints to etablish causality.