Background <p>Weight stigma causes significant physical and psychological harm to its targets.</p> Objective <p>This review aims to determine when identifying as a member of the higher-weight group exacerbates versus mitigates the adverse effects of weight stigma.</p> Methods <p>Searches were conducted on 10 January, 2025, using PsycInfo, Medline, Scopus, Web of Science, Embase, and CINAHL. Evidence was synthesised in terms of exacerbating versus protective effects of higher-weight social identity (as moderator/mediator) in the relationship between weight stigma and 18 distinct health outcomes. This review is registered on PROSPERO (ID: CRD42023415639).</p> Results <p>Fourteen studies met the inclusion criteria. Studies employing weight status measures to assess higher-weight social identity identified actual and self-perceived higher-weight as risk factors for anticipated rejection, dietary control challenges, increased physiological stress and greater functional disability following stigmatisation. Conversely, studies measuring individual connection with the higher-weight group revealed that stronger identification had protective effects on self-esteem and distress, but only for specific individuals (e.g., those with low internalised weight bias).</p> Limitations <p>Grey literature and unpublished studies were not reviewed.</p> Conclusions <p>Initial evidence suggests that higher-weight social identity functions as both risk and protective factor in the relationship between weight stigma and well-being.</p> Implications <p>Future research should explore the emotional and evaluative components of higher-weight social identity to enhance understanding of how and when group membership influences the adverse effects of weight stigma. This knowledge can inform targeted interventions designed to improve the well-being of higher-weight individuals.</p>