Emotion mobilizes and demobilizes a social movement while the movement itself impacts people's emotions. An evidence base is needed for developing timely emotion-focused counseling services for affected populations worldwide. This experience sampling study investigated the impact of a social movement on everyday emotional reactivity, variability, instability, and persistence, and whether and how these predicted subsequent psychological distress and well-being among 108 community-dwelling adults. Fifty-four participants reported momentary events and emotions 5 times daily over 7 days during the Umbrella Movement in Hong Kong. An age-matched, sex-matched comparison group (n = 54) participated during a period without major social/political movement. Psychological distress and well-being were assessed at baseline (Time 1 [T1]) and 3-month follow-up (Time 2 [T2]). Hierarchical linear modeling revealed lower valence ratings of positive events during the Umbrella Movement. Lower positive emotional reactivity and higher negative emotional reactivity in positive events were reported during the movement. Controlling for demographics and T1 scores, the positive association between negative emotional reactivity in positive events and T2 depressive symptoms, and the inverse association between positive emotional instability and T2 positive emotions, were significant only among the comparison group. The positive association between positive emotions in positive events and T2 life satisfaction was significant only among the Umbrella Movement group. People could experience significant changes in their emotions in everyday life during a social movement, even if it is short and relatively nonviolent like the Umbrella Movement. Maximizing positive emotions in positive events during a social movement can uniquely contribute to higher subsequent psychological well-being. (PsycINFO Database Record