BackgroundCommon mental disorders are the leading cause of workplace absences. While the reasons for this are multifarious, there is little doubt that stigma related to common mental disorder plays a large role in sickness absence and in poor help-seeking. Frequently both managers and staff are unsure of how to approach and intervene with mental health related problems. We have therefore devised a mental health intervention programme (Prevail) that aims to reduce stigma and to educate staff about evidence-based low intensity psychological interventions. These can be used by the individual, as well as in collaboration with managers via co-production of problem-focussed solutions, with the aim of improving mental health, reducing sickness absence, and increasing workplace productivity.MethodsThis two-armed cluster randomised control trial (RCT) will evaluate the effectiveness of Prevail. Eighty managers at a large UK government institution (the DVLA) and their teams (approximately 960 employees) will be randomised into the active intervention group or control (employment as usual) arms of the study. All participants will be invited to complete a series of questionnaires related to mental health stigma, their current and past mental health, and their recent workplace productivity (absenteeism and presenteeism). All employees in the active arm will receive the Prevail Staff intervention, which covers stigma reduction and includes psychoeducation about evidence-based low intensity psychological interventions for common mental disorder. The managers in the active arm will also receive the Prevail Managers programme which covers communication skills, problem formulation, and problem-solving skills. The questionnaire battery will then be given to both groups again 4 weeks post training, and 12 months post-training. Official records of absenteeism from Human Resources will also be gathered from both active and control groups at 12 months post-training.DiscussionThe treatment trial aims to evaluate if Prevail reduces mental health related stigma (of a number of forms), increases help-seeking behaviours, and increases workplace productivity (via decreased absenteeism and presenteeism).Trial registrationISRCTN12040087. Retrospectively registered 04/05/2020.