The aim of the present study was to investigate the mediating role of life expectancy in the relationship between family functioning and mental health among university students. In a correlational design, a total of 392 students from the University of Kurdistan (Sanandaj, Iran) were selected through convenience sampling during the second semester of the 2022–2023 academic year. Data were collected using the Mental Health Continuum-Short Form (MHC-SF), the Snyder Hope Scale (SHS), and the McMaster Family Assessment Device (FAD). The findings indicated that there were positive and significant relationships between dimensions of family functioning, life expectancy, and mental health (P < 0.01). The path analysis model demonstrated a good fit. All direct effects of family functioning dimensions on life expectancy and mental health were statistically significant (P < 0.05). Furthermore, the examination of indirect effects revealed that the indirect effect of family functioning dimensions on mental health through life expectancy was statistically significant (P < 0.05). Accordingly, it appears that healthy family functioning enhances students' mental health by increasing their life expectancy.