Abstract: Military service members admitted to inpatient psychiatry for self-injurious thoughts and behaviors (SITBs) represent an at-risk group for continued SITBs and rehospitalizations in the post-hospital discharge period. Yet, there is a paucity of evidence-based interventions designed to be delivered on inpatient psychiatric units to reduce the risk of post-discharge SITBs. To address this gap, our group developed Written Exposure Therapy for Suicide Prevention (WET-SP), which is based on the written disclosure paradigm. This paper describes the design, methodology, and protocol of a randomized controlled trial. The primary objective of this study is to evaluate the efficacy of a novel, brief, scalable, cognitive behavioral therapy-WET-SP-in reducing the incidence and severity of SITBs in active duty military service members, veterans, and their adult military beneficiaries following a psychiatric hospitalization due to suicide ideation, suicide plans, or a suicide attempt.