The purpose of this paper is to examine the impact of high-performance human resource management practices (HPHRMPs) on organisational citizenship behaviour (OCB) and the influences of national culture (NC) and organisational culture (OC) on this relationship. Design/methodology/approach: Using a self-administered survey, data were collected from a sample of 420 public sector employees. The hypotheses were tested using structural equation modeling and hierarchical regression analysis. Findings: The findings of this study offer new insights into the ability to improve OCB through greater consideration of NC and OC in the design of HPHRMP. The results indicated that NC fully mediates the relationship between HPHRMP and OCB, whilst OC has a partial mediating influence. Research limitations/implications: HPHRMP includes a wide variety of functional areas; however, this study has only examined three (reward management, performance appraisal and promotion practices) and contributes to understanding the importance of institutional theory in HRM. Practical implications: This study highlights the need for HR professionals to ensure that they consider the impact of cultural differences (national and organisational) on how these HR practices will be perceived by employees. Originality/value: The present study seeks to extend research into the link between cultural context and HPHRMP and posits that culture plays a crucial role in this relationship.