INTRODUCTION: Melasma is a pigmentation disorder of the skin. Characterised by brown to gray-brown patches on the face and neck, the condition predominantly affects women and has been associated with pregnancy, hormonal variation and sun exposure. Melasma can be disfiguring and anxiety-provoking, and quality of life is often adversely impacted. Management includes sun protection, laser and energy device therapy, topical and oral skin-bleaching agents and chemical peels. While clinical trials of melasma exist, there is a lack of consistency in reported outcomes, which has been a barrier to the aggregation of data in systematic reviews and meta-analyses. This protocol describes a planned process for development of a minimum set of outcomes (ie, 'core outcome set') that should be measured in all clinical trials of melasma. METHODS AND ANALYSIS: An exhaustive list of potential outcomes will be extracted from four sources: (1) systematic literature review of outcomes in clinical trials; (2) semistructured patient interviews; (3) brochures, pamphlets, clinical trial registries, and other published and unpublished sources and documentation; and (4) interviews with non-patient, non-physician stakeholders, including federal regulators, industry scientists and non-physician providers. An international two-round Delphi process will then be performed to identify the outcomes deemed most important to patients and physicians. Subsequently, a consensus meeting will be convened to review and process the results, and to vote on a final set of core outcomes. ETHICS AND DISSEMINATION: Ethics approval was provided by the Northwestern University Institutional Review Board (protocol ID: STU00201637). This study is registered with both the Core Outcome Measures in Effectiveness Trials and Cochrane Skin-Core Outcome Set Initiative initiatives, and this protocol is in accordance with the guidelines for protocol development of both groups. All findings from the study described in this protocol will be disseminated to all stakeholders involved in the development process and will be submitted for publication in peer-reviewed journals. PROSPERO REGISTRATION NUMBER: CRD42020214189.