Introduction This study developed a training intervention (‘GetREAL’) to change the practice of staff working in National Health Service inpatient mental health rehabilitation units in order to increase service users’ engagement in activities. Method The intervention was developed through eight consultation events and piloting in two settings, drawing on the expertise of occupational therapists, psychiatrists, organisational change specialists and service users, together with multi-disciplinary teams. Results A manual for the intervention, a fidelity checklist, an induction programme and training materials were produced. The intervention applied a three-stage change model (predisposing, enabling and reinforcing) and was informed by theories from occupational therapy and organisational development. It was delivered by psychiatrists, occupational therapists, activity workers and service users. Staff were encouraged to change their ward structures and routines as well as their practice. Clinical supervision and reflective practice were integral to the trainers’ regime. Conclusion The intervention was theoretically coherent, allied to practice and shown to be feasible to deliver. It offered tailored work-based training to the whole multi-disciplinary team, including support staff. Making activity central to rehabilitation could improve patients’ use of time and their consequent function and wellbeing. However, questions were raised about long-term sustainability of change processes.