Background Emerging evidence indicates that holding particular stress mindsets has favorable implications for peoples’ health and performance under stress. Purpose The aim of the current study was to examine the processes by which implicit and explicit stress mindsets relate to health- and performance-related outcomes. Specifically, we propose a stress beliefs model in which somatic responses to stress and coping behaviors mediate the effect of stress mindsets on outcomes. Methods Undergraduate university students (N  =  218, n = 144 females) aged 17– 25 years completed measures of stress mindset, physical and psychological wellbeing, perceived stress, perceived  somatic responses to stress, proactive behaviors under stress, and an implicit association test assessing an implicit stress mindset. At the end of the semester, students’ academic performance was collected from university records. Results Path analysis indicated significant indirect effects of stress mindset on psychological wellbeing and perceived stress through proactive coping behaviors and perceived  somatic symptoms. Stress mindset directly predicted perceived stress and physical wellbeing, and physical wellbeing and academic performance were predicted by stress mindset through perceived somatic symptoms. Implicit stress mindset did not predict proactive behavior as anticipated. Conclusions Current findings indicate that behaviors with the goal of proactively meeting demands under stress and perceived somatic symptoms are important mediators of the effect of stress mindset on health- and performance-related outcomes. The findings from this study provide formative data that can inform the development of future interventions aiming to encourage more adaptive responses to stress.