BackgroundNurses, midwives and paramedics comprise over half of the clinical workforce in the UK National Health Service and have some of the highest prevalence of psychological ill health. This study explored why psychological ill health is a growing problem and how we might change this.MethodsA realist synthesis involved iterative searches within MEDLINE, CINAHL and HMIC, and supplementary handsearching and expert solicitation. We used reverse chronological quota screening and appraisal journalling to analyse each source and refine our initial programme theory. A stakeholder group comprising nurses, midwives, paramedics, patient and public representatives, educators, managers and policy makers contributed throughout.ResultsFollowing initial theory development from 8 key reports, 159 sources were included. We identified 26 context–mechanism–outcome configurations, with 16 explaining the causes of psychological ill health and 10 explaining why interventions have not worked to mitigate psychological ill health. These were synthesised to five key findings: (1) it is difficult to promote staff psychological wellness where there is a blame culture; (2) the needs of the system often over-ride staff psychological well-being at work; (3) there are unintended personal costs of upholding and implementing values at work; (4) interventions are fragmented, individual-focused and insufficiently recognise cumulative chronic stressors; and (5) it is challenging to design, identify and implement interventions.ConclusionsOur final programme theory argues the need for healthcare organisations to rebalance the working environment to enable healthcare professionals to recover and thrive. This requires high standards for patient care to be balanced with high standards for staff psychological well-being; professional accountability to be balanced with having a listening, learning culture; reactive responsive interventions to be balanced by having proactive preventative interventions; and the individual focus balanced by an organisational focus.PROSPERO registration numberCRD42020172420.