This study examines the role of ethical leaders at a supervisory level in implementing high-performance work systems to influence employees’ citizenship behaviour by enhancing employee affective commitment. Specifically, the study explores the moderated mediation role of ethical leaders and the mediation role of affective commitment on the relationship between high-performance work systems and organisational citizenship behaviours in two large tertiary public hospitals in Pakistan. Employing a case study approach, survey data were gathered from 266 and 548 front-line doctors and nurses from the two large public tertiary care hospitals. SPSS and AMOS were used for data cleaning and analysis, Structural Equation Modelling was also deployed for hypotheses testing. Our findings suggest that in both hospitals, affective commitment positively mediated the relationship between high-performance work systems and organisational citizenship behaviour. Second, affective commitment positively mediated the relationship between ethical leadership and organisational citizenship behaviour. However, the role of ethical leadership at the supervisory level as a moderated-mediated hypothesis was significant in one hospital and insignificant in the other. These findings are discussed, and we draw conclusions that highlight theoretical, practical and managerial implications for the public healthcare sector in Pakistan.