Objective: Heterogeneous brief non-pharmacological interventions and guidelines exist to treat the burgeoning presentations to both emergency department and inpatient settings, for those in a crisis of mental ill-health. We systematically reviewed the literature to create a taxonomy of these brief non-pharmacological interventions, and review their evaluation methods and effectiveness. Method: We conducted a systematic review across Cochrane, CINAHL, DARE, Embase, MEDLINE, PsycINFO databases. Studies meeting quality criteria, using Joanna Briggs Institute tools, were eligible. Interventions were categorised, and outcomes synthesised. Results: Thirty-nine studies were included: 8 randomised controlled trials, 17 quasi-experimental, 11 qualitative studies, and 3 file audits. Taxonomy produced six coherent intervention types: Skills-focussed, Environment-focussed, Special Observation, Psychoeducation, Multicomponent Group and Multicomponent Individual. Despite this, a broad and inconsistent range of outcome measures reflected different outcome priorities and prevented systematic comparison of different types of intervention or meta-analysis. Few brief non-pharmacological interventions had consistent evidential support: sensory modulation rooms consistently improved distress in inpatient settings. Short admissions may reduce suicide attempts and readmission, if accompanied by psychotherapy. Suicide-specific interventions in emergency departments may improve depressive symptoms, but not suicide attempt rates. There was evidence that brief non-pharmacological interventions did not reduce incidence of self-harm on inpatient wards. We found no evidence for frequently used interventions such as no-suicide contracting, special observation or inpatient self-harm interventions. Conclusion: Categorising brief non-pharmacological interventions is feasible, but an evidence base for many is severely limited if not missing. Even when there is evidence, the inconsistency in outcomes often precludes clinicians from making inferences, although some interventions show promise.