Background: Research in psychology has attempted to identify the main predictors and strategies that are useful to promote well-being. Although personality has been recognized as one of the main determinants of well-being, the primary mechanisms involved in this relationship are not fully disclosed. This research addressed the impact of pro-environmental behaviors in the interplay between the Big Five (openness, extraversion, agreeableness, conscientiousness, and neuroticism) and psychological well-being (eudaimonic). Methods: A total of 176 young adults (mean age = 21.55 years; SD age = 1.76 years; 114 F; mean education = 14.57 years; SD = 2.11 years) participated in this study. The participants were requested to complete a short battery of self-report questionnaires, including the Big Five Inventory-10, the Pro-environmental Behavior Questionnaire, and the Psychological Well-being Scale. Results: The results revealed that pro-environmental behaviors only mediated the association between agreeableness and eudaimonic well-being (B = 2.25, BootSE = 1.26, BootCIs 95% [0.149, 5.050]). Conclusions: These findings contributed to identifying the potential mechanisms through which personality contributes to individual eudaimonic well-being, also providing insights into the development of promoting interventions based on eco-sustainable behaviors. Limitations and future research directions are discussed.