Caregivers are integral to health and social care systems in South Asian countries yet are themselves at higher risk of mental illness. Interventions to support caregiver mental health developed in high-income contexts may be contextually inappropriate in the Global South. In this mixed-methods study, we evaluated the implementation and scaling of a locally developed mental health group intervention for caregivers and others in Uttarakhand, India. We describe factors influencing implementation using the updated Consolidated Framework for Implementation Research, and selected implementation outcomes. Key influencing factors we found in common with other programs included: an intervention that was relevant and adaptable; family support and stigma operating in the outer setting; training and support for lay health worker providers, shared goals, and relationships with the community and the process of engaging with organisational leaders and service users within the inner setting. We identified further factors including the group delivery format, competing responsibilities for caregivers and opportunities associated with the partnership delivery model as influencing outcomes. Implementation successfully reached target communities however attrition of 20% of participants highlights the potential for improving outcomes by harnessing enablers and addressing barriers. Findings will inform others implementing group mental health and caregiver interventions in South Asia.