In this diary study, we consider shared leadership and team workload as antecedents of team mental health. We draw on conservation of resources theory to theorize how linear change trajectories of shared leadership are related to change trajectories in team members’ shared well-being and emotional exhaustion. Furthermore, we investigate the interaction between change trajectories of shared leadership and team workload, predicting that change in shared leadership will be more strongly related to change in team mental health when team workload increases. 265 team members nested in 77 teams completed a daily diary survey over five consecutive workdays. As hypothesized, an increase in shared leadership was associated with an increase in team well-being and a decrease in emotional exhaustion over time. Further, shared leadership interacted with team workload, such that an increase in shared leadership was more strongly associated with a decrease in shared emotional exhaustion when team workload increased. However, team member well-being was not affected by such an interaction. These findings address the missing link between shared leadership and team well-being and exhaustion, establish shared leadership as an important team resource, and contribute a temporal perspective on shared leadership as a dynamic team phenomenon.