Social interactions and active activities are key to psychological wellbeing, but how do these activities improve wellbeing? Building on work showing that positive emotional experiences help build psychological resources, we test the prediction that momentary positive emotional experiences mediate the relationships between social interactions, active activities, and wellbeing. In a pre-registered experience sampling study, 106 participants reported their wellbeing, momentary emotional experiences, and activities linked to intense emotions five times per day for 15 days (7,110 observations). Participants reported experiencing more intense positive emotions when interacting with others (especially face-to-face), and when engaged in active (versus passive) activities. As predicted, positive emotional experiences partially mediated the positive relationships between social interactions and wellbeing, and between active activities and wellbeing (explaining 25% and 12% of variance, respectively). These findings show that intense emotional experiences can be elicited by social and active activities, helping explain how these activities aid our psychological wellbeing.