BACKGROUND: There are increasing efforts for the integration of mental health services into primary care settings in low- and middle-income countries. However, commonly used approaches to train primary care providers (PCPs) may not achieve the expected outcomes for improved service delivery, as evidenced by low detection rates of mental illnesses after training. One contributor to this shortcoming is the stigma among PCPs. Implementation strategies for training PCPs that reduce stigma have the potential to improve the quality of services. DESIGN: In Nepal, a type 3 hybrid implementation-effectiveness cluster randomized controlled trial will evaluate the implementation-as-usual training for PCPs compared to an alternative implementation strategy to train PCPs, entitled Reducing Stigma among Healthcare Providers (RESHAPE). In implementation-as-usual, PCPs are trained on the World Health Organization Mental Health Gap Action Program Intervention Guide (mhGAP-IG) with trainings conducted by mental health specialists. In RESHAPE, mhGAP-IG training includes the added component of facilitation by people with lived experience of mental illness (PWLE) and their caregivers using PhotoVoice, as well as aspirational figures. The duration of PCP training is the same in both arms. Co-primary outcomes of the study are stigma among PCPs, as measured with the Social Distance Scale at 6 months post-training, and reach, a domain from the RE-AIM implementation science framework. Reach is operationalized as the accuracy of detection of mental illness in primary care facilities and will be determined by psychiatrists at 3 months after PCPs diagnose the patients. Stigma will be evaluated as a mediator of reach. Cost-effectiveness and other RE-AIM outcomes will be assessed. Twenty-four municipalities, the unit of clustering, will be randomized to either mhGAP-IG implementation-as-usual or RESHAPE arms, with approximately 76 health facilities and 216 PCPs divided equally between arms. An estimated 1100 patients will be enrolled for the evaluation of accurate diagnosis of depression, generalized anxiety disorder, psychosis, or alcohol use disorder. Masking will include PCPs, patients, and psychiatrists. DISCUSSION: This study will advance the knowledge of stigma reduction for training PCPs in partnership with PWLE. This collaborative approach to training has the potential to improve diagnostic competencies. If successful, this implementation strategy could be scaled up throughout low-resource settings to reduce the global treatment gap for mental illness. TRIAL REGISTRATION: ClinicalTrials.gov, NCT04282915 . Date of registration: February 25, 2020.