BackgroundStigma associated with substance use and criminal involvement is pervasive and creates a barrier to evidence-based addiction care within the criminal legal system. Research has yet to examine a multi-level stigma intervention which targets the intersection of these stigmas among both criminal legal staff and legally-involved clients.MethodsThis paper presents the protocol for a non-randomized trial of a multi-level stigma intervention called Combatting Stigma to Aid Reentry and Recovery (CSTARR) that involves two interventions: (1) training for criminal legal staff to address public stigma and (2) group-based acceptance and commitment therapy to address self-stigma among legally-involved adults enrolled in substance use treatment. Staff and client participants are engaged with a program called the Tennessee Recovery Oriented Compliance Strategy in 6 East Tennessee counties. This study examines the feasibility, acceptability, and preliminary effectiveness of CSTARR using a type 1 hybrid implementation/effectiveness trial with pre to post follow-up.DiscussionStigma must be addressed in the criminal legal system to facilitate the uptake of evidence-based addiction care. This study is the first to evaluate a stigma intervention designed for the criminal legal setting and results will be used to inform a larger, randomized controlled trial. The rationale for this study, research design and measures, as well as potential implications for the field are described.Trial registrationThis clinical trial is registered at clinicaltrials.gov with the identifier NCT05152342. Registered 11/5/2021 athttps://register.clinicaltrials.gov/prs/app/action/SelectProtocol?sid=S000BIN8&selectaction=Edit&uid=U0005X4C&ts=2&cx=-u3wsbx.