Mental health crises cause significant distress and disruption to the lives of individuals and their families. Community crisis care systems are complex, often hard to navigate and poorly understood. This realist evidence synthesis aimed to explain how, for whom and in what circumstances community mental health crisis services for adults work to resolve crises and is reported according to RAMESES guidelines. Using realist methodology, initial programme theories were identified and then tested through iterative evidence searching across 10 electronic databases, four expert stakeholder consultations and n = 20 individual interviews. 45 relevant records informed the three initial programme theories, and 77 documents, were included in programme theory testing. 39 context, mechanism, outcome configurations were meta-synthesized into three themes: (1) The gateway to urgent support; (2) Values based crisis interventions and (3) Leadership and organizational values. Fragmented cross-agency responses exacerbated staff stress and created barriers to access. Services should focus on evaluating interagency working to improve staff role clarity and ensure boundaries between services are planned for. Organizations experienced as compassionate contributed positively to perceived accessibility but relied on compassionate leadership. Attending to the support needs of staff and the proximity of leaders to the front line of crisis care are key. Designing interventions that are easy to navigate, prioritize shared decision-making and reduce the risk of re-traumatizing people is a priority.