Objective To develop an international consensus statement to advise on designing, delivering and evaluating sport-based interventions (SBIs) aimed at promoting social, psychological and physical well-being in prison. Design Modified Delphi using two rounds of survey questionnaires and two consensus workshops. Participants A multidisciplinary panel of more than 40 experts from 15 international jurisdictions was formed, including representation from the following groups and stakeholders: professionals working in the justice system; officials from sport federations and organisations; academics with research experience of prisons, secure forensic mental health settings and SBIs; and policy-makers in criminal justice and sport. Results A core research team and advisory board developed the initial rationale, statement and survey. This survey produced qualitative data which was analysed thematically. The findings were presented at an in-person workshop. Panellists discussed the findings, and, using a modified nominal group technique, reached a consensus on objectives to be included in a revised statement. The core research team and advisory board revised the statement and recirculated it with a second survey. Findings from the second survey were discussed at a second, virtual, workshop. The core research team and advisory board further revised the consensus statement and recirculated it asking panellists for further comments. This iterative process resulted in seven final statement items; all participants have confirmed that they agreed with the content, objectives and recommendations of the final statement. Conclusions The statement can be used to assist those that design, deliver and evaluate SBIs by providing guidance on: (1) minimum levels of competence for those designing and delivering SBIs; (2) the design and delivery of inclusive programmes prioritising disadvantaged groups; and (3) evaluation measures which are carefully calibrated both to capture proposed programme outcomes and to advance an understanding of the systems, processes and experiences of sport engagement in prison.