Purpose This paper aims to examine the link between spirituality, work-life integration, work passion and mental health among millennial employees. It also tests the mediating effect of the dualistic model of work passion in the framework. Design/methodology/approach A cross-sectional quantitative design was adopted using samples of 167 millennial employees from the education and service sectors. Results were analysed using Statistical Package of Social Science, Process macro extension and AMOS modelling software. Findings The findings indicated that millennials’ spirituality was positively linked to harmonious passion, while work-life integration was positively linked with obsessive and high mental health symptoms. Mediating effects were also discovered in which harmonious passion fully mediated the positive relationship between spirituality and mental health symptoms. While obsessive passion partially mediated work-life integration and mental health symptoms. Originality/value This paper highlights the mediating influence of millennials’ work passion for explaining their mental health symptoms. It also suggests the practicality and essential roles of spirituality and work-life integration in managing the mental health of existing and future millennials in the workforce.