There has been a noticeable increase in the prevalence of mental health issues, prompting research into the relationship between mental health and people's implicit theories about their intelligence, or their mindsets. This study investigated the relationships between mindset, well-being, and depressive symptoms. A positive relationship between a fixed mindset and depressive symptomatology (H1) was hypothesised. Additionally, H2 assumed that well-being and mindset were good predictors of depressive symptomatology. The study comprised a sample of 874 users of the Slovene online platform 'Positive Psychology for a Better Life'. The online survey included measures of mindset (the Revised Implicit Theories of Intelligence (Self-Theory) Scale), well-being (the Mental Health Continuum-Short Form [MHC-SF]), and depressive symptomatology (the Center for Epidemiologic Studies Depression Scale [CES-D]). The results showed a positive correlation between a fixed mindset and depressive symptomatology, thus supporting H1. To test whether well-being and mindset are good predictors of depressive symptomatology, discriminant analysis was performed. There was a significant effect of the independent variables on the dependent variable. The model correctly classified 76.9% of participants based on their personal and social antecedents of well-being and mindset, as measured by CES-D scale scores, so H2 was also supported. In conclusion, mindset is reflected in one's perception of mental health. Therefore, it is crucial to create growth mindset initiatives and curricula in education. Our analysis shows that the MHC-SF and Implicit Self-Theory scales are adequate for predicting depression in Positive Psychology Platform users. These findings could stimulate future research in this area.