Background Fatigue is common among mothers of infants and young children and associated with a range of negative parenting outcomes. Little is understood, however, about the mechanisms by which fatigue may impact on parenting, particularly among mothers beyond 12 months post‐partum. This study investigated the relationship between maternal fatigue and overreactive discipline, and whether parenting self‐efficacy mediates this relationship. Methods Participants were 252 Australian mothers of 1–4 years old children. Levels of fatigue, parenting self‐efficacy, and overreactive discipline were recorded via a self‐report questionnaire. Results A simple mediation model analysis provided support for the direct effect of fatigue on overreactive discipline, as well as the mediation of this relationship by parenting self‐efficacy. Conclusions These findings suggest fatigue may contribute to overreactive discipline in mothers of young children via two pathways: directly, and indirectly via parenting self‐efficacy. Interventions that support mothers to manage fatigue and maintain a sense of parenting self‐efficacy while facing ongoing exhaustion may promote the use of more effective and less adverse discipline responses with children.