Despite international commitment to achieving the end of HIV as a public health threat, progress is off-track and existing gaps have been exacerbated by COVID-19's collision with existing pandemics. Born out of models of political accountability and historical healthcare advocacy led by people living with HIV, community-led monitoring (CLM) of health service delivery holds potential as a social accountability model to increase the accessibility and quality of health systems. However, the effectiveness of the CLM model in strengthening accountability and improving service delivery relies on its alignment with evidence-based principles for social accountability mechanisms. We propose a set of unifying principles for CLM to support the impact on the quality and availability of health services. Building on the social accountability literature, core CLM implementation principles are defined. CLM programmes include a community-led and independent data collection effort, in which the data tools and methodology are designed by service users and communities most vulnerable to, and most impacted by, service quality. Data are collected routinely, with an emphasis on prioritizing and protecting respondents, and are then be used to conduct routine and community-led advocacy, with the aim of increasing duty-bearer accountability to service users. CLM efforts should represent a broad and collective community response, led independently by impacted communities, incorporating both data collection and advocacy, and should be understood as a long-term approach to building meaningful engagement in systems-wide improvements rather than discrete interventions. The CLM model is an important social accountability mechanism for improving the responsiveness of critical health services and systems to communities. By establishing a collective understanding of CLM principles, this model paves the way for improved proliferation of CLM with fidelity of implementation approaches to core principles, rigorous examinations of CLM implementation approaches, impact assessments and evaluations of CLM's influence on service quality improvement.