<p>This study explored the predictive roles of Basic Psychological Needs Satisfaction (BPNS) and Peace of Mind (PoM) in shaping subjective well-being—defined through positive and negative affect—among university students in Greece. Based on Self-Determination Theory (SDT), the research examined how the fulfillment of autonomy, competence, and relatedness contributes to students’ affective states, while also assessing the unique contribution of PoM as a psychological strength. A sample of 383 students completed standardized questionnaires measuring need satisfaction, PoM, and positive and negative affect. Correlational analyses showed that competence and relatedness were positively associated with positive affect, while autonomy and competence were negatively associated with negative affect. Hierarchical multiple linear analyses revealed that PoM significantly predicted both affective outcomes, accounting for incremental variance in positive and negative affect beyond that explained by basic psychological needs. Specifically, higher levels of PoM were predictors of higher positive emotions and lower negative ones. These findings suggest that PoM appears to function as an important emotional resource in academic settings, associated with well-being. Despite its limitations, the study highlights the importance of fostering both the satisfaction of students’ psychological needs and their inner sense of peace through interventions such as mindfulness training and autonomy-supportive educational practices, considering culturally informed programs as well.</p>