Weight stigma is a pervasive social problem that can negatively impact the health and well-being of stigmatized individuals. The present study used ecological momentary assessment (EMA) to assess the motivational consequences of weight stigma in people’s everyday lives. Forty-six community adults (22 men, 24 women) completed baseline measures of prior stigma experiences and internalized weight bias before taking part in the EMA component of the study. Over a 2-week period, participants recorded their experiences with weight stigma immediately after they occurred, and also reported their current mood and motivation to diet, exercise, and lose weight. At the end of each day, participants again reported their mood and motivation to diet, exercise, and lose weight. Participants experienced weight stigma almost once per day, on average, indicating that stigma experiences are common in people’s everyday lives. At the episode level, lower positive affect (PA) following a stigma experience was associated with lower motivation to diet, exercise, and lose weight, but only for women, individuals high in prior experiences with stigma, and individuals high in internalized weight bias. We also found that the more frequently people experienced stigma on a given day, the less motivated they were to diet, exercise, and lose weight at the end of the day. Furthermore, these associations were mediated by low PA. These findings highlight the deleterious nature of stigma experiences, and can also inform public health and intervention efforts to reduce the negative impact of stigma and improve the well-being of affected individuals.