This study analysed the impact of employees’ organisational justice perception (OJP) on their engagement in organisational citizenship behaviour (OCB) within tertiary educational institutions in Ghana. Furthermore, the study investigated the mediating effect of employee happiness on the relationship between OJP and OCB among employees in tertiary educational institutions in Ghana. A total of 394 respondents from 27 tertiary institutions in Ghana participated in the survey through the administration of questionnaires. The study employed Structural Equation Modelling to examine the hypothesised relationships and Andrews Hayes’ Process Model was utilised for mediation analysis. The results indicated that the level of employee happiness in the workplace is a substantial and positive indicator of OCB and served as a full mediator in the link between OJP and OCB. The study recommended that the management of tertiary educational institutions and human resource management practitioners should develop evidence-based interventions aimed at boosting employee well-being and promoting positive perceptions of organisational justice.