The pursuit of sustainable well-being has placed increasing emphasis on the role of leadership and personality in shaping individual flourishing. This study investigates the relationships between Human Capital Sustainability Leadership (HCSL), Big Five of Personality Traits Inventory, and Flourishing Scale. Grounded in positive psychology and sustainable leadership theory, the study explores whether the Big Five personality factors (extraversion, agreeableness, conscientiousness, openness, and neuroticism) mediate the relationship between HCSL and flourishing. A total of 429 participants completed validated measures of leadership, personality, and flourishing. Mediation analyses were conducted using the PROCESS macro (Model 4; Hayes, 2022). Across all models, leadership styles positively predicted flourishing. Conscientiousness emerged as a consistent positive mediator in the HCSL and mindful leadership models, with a marginal effect in the sustainable and servant leadership models. Extraversion, agreeableness, and openness were significant positive predictors of flourishing, whereas neuroticism negatively predicted flourishing, although they did not serve as mediators of the leadership-flourishing link. The integrated findings suggest that leadership fosters flourishing primarily through direct effects, with conscientiousness playing a unique mediating role. These results highlight the importance of both leadership and personality traits in understanding pathways to flourishing.