Following the Job Demands-Resources model’s motivational process, this study investigates the role of person-organisation fit and work engagement as mediating processes between ethical culture and employee commitment, where ethical culture is seen as an organisational resource. It was expected that the stronger the ethical values and practices are experienced to be, the more compatible employees feel with the organisation. A good person-organisation fit was further hypothesised to act as a personal job resource for the employees, who would consequently experience higher work engagement leading to stronger affective commitment and less turnover intentions. The study used questionnaire data gathered from 270 Finnish school psychologists. The analyses were performed by using SEM and mediation modelling with the bootstrapping method. Ethical organisational culture had a significant positive association with experienced person-organisation fit, which in turn was related to higher work engagement. Both person-organisation fit and work engagement were associated with higher affective commitment and with lower turnover intentions. This study contributes to understanding the mechanisms through which ethical culture affects employee commitment by integrating the concept of person-organisation fit with the Job Demands-Resources model. Organisations can retain committed and motivated workforce through fostering a strong ethical culture, which can support employees’ affective commitment to the organisation.