Aims To examine the barriers and facilitators to effective operation of a regional tobacco control coordinator working within and across criminal justice and public health, whose goal was to raise tobacco control awareness and support the development of smoking cessation treatment for offenders. Design A reflexive, mixed-methods case study approach using in-depth interviews, project reports and observation of advisory board meetings. Setting The coordinator worked with prisons, probation and police custody, where there are high levels of social disadvantage and smoking. Participants Interviews (n = 34) at different stages of project with the coordinator, project advisers and local stakeholders from criminal justice and public health. Measurements Analysis of facilitators and barriers and the coordinator role from different perspectives. Findings Readiness to develop cessation services was a critical predictor of different criminal justice settings' engagement with the coordinator role. The coordinator enhanced cessation service delivery in individual prisons where there was a requirement and infrastructure in place to provide such services. In police custody, where there was no central guidance or pre-existing requirements, efforts to establish smoking cessation on the local agenda proved ineffective. In probation settings, the coordinator documented examples of good practice and supported brief intervention training. Variability in willingness to engage limited the project's ability to create joined-up working across criminal justice settings. Conclusions In the English criminal justice system, the prison service appears to provide a favourable context for development of smoking cessation support and a means of accessing hard-to-reach groups. Other criminal justice settings, most specifically police custody, appear less responsive to such activity. A coordinator role can improve smoking cessation support in the prison setting, and develop local improvements in tobacco control interventions in other settings such as probation, but as configured here, does not have the capacity to effect change across the criminal justice system.