Introduction: In nursing, identifying factors encouraging positive work attitudes is extremely important since a nurse’s performance directly impacts the quality of the care they provide, and, therefore, their patients’ health. Objective: The main objective of this research is to analyze whether the supervisor–nurse relationship is positively correlated with a nurse’s organizational citizenship behaviors. Thus, we established a main hypothesis as follows: the quality of the supervisor–nurse interpersonal relationship is positively related to the job satisfaction of the nurse, controlled by moderating the effects of psychological empowerment, the perceived organizational support, and leader–leader exchange. Methodology: This is a cross-sectional descriptive study with individuals as the units of analysis. The population studied comprised all the nurses and supervisors working in nine public hospitals in the autonomous community of Aragon (Spain). The sample consisted of 2541 nurses, 192 supervisors, and 2500 paired dyads. Self-report questionnaires were used to ensure workers’ anonymity. The dependent variable was the nurse’s organizational citizenship behaviors; the main independent variable was the supervisor’s leadership; the moderating variables were the nurse’s empowerment, the organizational support the nurse perceived, and the quality of the supervisor–superior relationship. Results: Empirical evidence demonstrates that the quality of the supervisor–nurse relationship is positively correlated with organizational citizenship behaviors. The results also confirm the moderating effect of nurses’ empowerment and of the organizational support they perceive. Discussion: Our research shows how important it is for organizations to establish management practices promoting high-quality nurse–supervisor relationships; thus, hospital management should monitor both the supervisors’ performance and leadership. Conclusions: The quality of the relationship the supervisor establishes with their nurses is vitally important since it is a necessary requirement for beneficial results for the organization as a result of citizenship behavior practice.