Background Employees who describe themselves as happy in their work are more likely to be motivated to fulfil their professional duties. Therefore, it is important that healthcare organisations and managers understand how to promote a sense of happiness among nurses.

Aim To investigate the relationship between the concepts of psychological capital, interactional justice, supervisor support and workplace happiness, and how they are mediated by employees’ trust in their supervisors.

Method Self-report questionnaires were used to obtain data from nurses on the variables of trust in supervisor, psychological capital, interactional justice, supervisor support and happiness at work. The questionnaires were distributed to 250 nurses working in hospitals in the city of Hamedan, Iran, and a total of 200 respondents completed and returned them. The data were then applied to a proposed model for promoting employees’ workplace happiness, which was evaluated using data analysis software.

Results The results showed that the model correctly identified a pathway for promoting workplace happiness in nurses. Moreover, it was found that psychological capital, interactional justice and supervisor support led to improved workplace satisfaction through the mediating role of nurses’ trust in their supervisors.

Conclusion The findings of this study indicate that paying attention to employees’ psychological capital, interactional justice and supervisor support, as well maintaining employees’ trust in their supervisors, could assist healthcare organisations and managers to achieve organisational targets such as increased job satisfaction.