The present study, based on broaden–and–build theory, examines the relationship between study–related positive emotions and academic performance, and the mediating role of psychological capital in this relationship. A sample of 639 Chilean high school students between 14 and 17 years old was used. Through structural equation modelling (SEM),—as hypothesized—a statistically significant indirect effect was found between study–related positive emotions and academic performance via psychological capital. Students’ study–related positive emotions were related to better academic performance through positive relationships with their levels of psychological capital (i.e., efficacy, hope, optimism, and resilience). Theoretical and practical implications of the results are discussed, limitations are mentioned, and future research directions are proposed.