<b><i>Objective:</i></b> Certain psychological and emotional factors can undermine attempts at weight management. Previously we have found that shame and self-criticism were significantly associated with disinhibition and perceived hunger in 2,236 participants of a weight management programme. This effect was fully mediated through weight-related negative affect. The present study examined the impact of self-criticism and self-reassurance on well-being and whether it was mediated by weight-related affect in the same population. <b><i>Methods:</i></b> Participants completed an online survey of measures of self-criticism and self-reassurance, and negative and positive affect associated with weight and well-being. <b><i>Results:</i></b> Path analysis suggested that self-criticism was significantly associated with decreased well-being, both directly and indirectly, mediated by increased negative and decreased positive weight-related affect. Self-reassurance had a stronger association with increased well-being by predicting lower negative and increased positive weight-related affect. All effects were significant at p < 0.001. <b><i>Conclusion:</i></b> Self-criticism and self-reassurance were related to well-being in participants attempting to manage their weight, both directly and through their impact on weight-related affect. The positive association between self-reassurance and well-being was stronger than the negative association between self-criticism and well-being. Supporting the development of self-reassuring competencies in weight management programmes may improve weight-related affect and well-being.