This study focuses on emerging adults’ personal agency, an individual feature associated with enhanced adaptive and resilient developmental trajectories. The two objectives were to explore the role of demographic, psychosocial risk, and relational factors in predicting personal agency and analyze whether romantic attachment mediates the connection between parental attachment and personal agency. The sample consisted of 607 Portuguese emerging adults aged between 18 and 30 years. Structural equation modeling results suggest that men are more likely to exhibit higher levels of personal agency than women. Trustful romantic relations and good paternal emotional bonds are associated with greater personal agency, while dependent romantic relations and maternal relations, characterized by inhibition of exploration, are associated with lower personal agency. Moreover, in romantic relations, trust, unlike dependence, partially mediates the association between parental attachment and personal agency. These findings are discussed based on attachment and self-determination theories, considering the importance of secure relationships for agency and autonomy in personal actions. This study provides important evidence for the influencers and mediators of personal agency, contributing to a better understanding of this individual capacity.