Abstract: Background: Many post-9/11 U.S. combat Veterans experience difficulty readjusting to civilian life after military service, including relationship problems, reduced work productivity, substance misuse, and increased anger control problems. Mental health problems are frequently cited as causing these difficulties, driven by unparalleled rates of mild traumatic brain injury, posttraumatic stress, and other co-occurring emotional and physical conditions. Given the high prevalence of multimorbidity in this cohort, acceptable, non-stigmatizing, transdiagnostic interventions targeting reintegration are needed. The STEP-Home reintegration workshop has the potential to significantly improve skills to foster civilian reintegration, increase engagement in VA services, and improve mental health outcomes in Veterans with and without diagnosed clinical conditions. Methods/design: Ongoing from 2019, a prospective, two-site, randomized trial of 206 post-9/11 U.S. military Veterans randomized to receive either 12 sessions of the STEP-Home transdiagnostic reintegration workshop (SH; Active Intervention) or Present Centered Reintegration Group Therapy (PCRGT; Active Control Intervention). Primary outcomes are reintegration, anger, and emotional regulation post-intervention and at 3-months post-intervention. Secondary outcomes include measures of mental health, functional and vocational status, and cognition. Conclusion: This study addresses an important gap in transdiagnostic interventions to improve civilian reintegration in post-9/11 Veterans. STEP-Home is designed to promote treatment engagement and retention, opening the door to critically needed VA care, and ultimately reducing long-term healthcare burden of untreated mental health illness in U.S. Veterans.