INTRODUCTIONThe age-standardised suicide mortality rate in Thailand has been stable at a high level in recent years, highlighting the need for suicide prevention interventions. In Thailand, community involvement plays a key role in health promotion. The aim of this ongoing trial is to evaluate the efficacy of a community participatory intervention in two subdistricts in Thailand for reducing suicidality symptoms among individuals considered at high risk for suicide and compare the outcomes to two control subdistricts.METHODS AND ANALYSISIn this cluster (subdistrict) randomised controlled trial, we randomised two districts to either the community participatory intervention arm or the control arm. From each district, we selected one large and one small subdistricts. We estimated that we need 235 participants per study arm, who were recruited from subdistrict health centres. The primary outcome is suicidality symptoms. Secondary outcomes are depression symptoms, quality of life, stress level and health and community service accessibility.ETHICS AND DISSEMINATIONThis trial has been approved by the Research Ethics Committee, Faculty of Nursing, Chiangmai University (number 050/2022). All participants were required to provide informed consent. The findings of the study will be disseminated in peer-reviewed journals and via conferences.TRIAL REGISTRATION NUMBERTCTR20220620003; the Thai Clinical Trials Registry.