RATIONALE: Workplace health and wellbeing practices (WHWPs) often fail to improve psychological health or wellbeing because of implementation failure. Thus, implementation should be evaluated to improve the effectiveness of WHWPs. OBJECTIVE: We conducted a systematic review to identify critical success factors for WHWP implementation and gaps in the evidence. Doing so provides a platform for future theoretical development. METHODS: We reviewed 74 separate studies that assessed the implementation of WHWPs and their effects on psychological health or psychological wellbeing. Most studies were from advanced industrial Western democracies (71). Intervention types included primary (e.g., work redesign, 37 studies; and health behavior change, 8 studies), secondary (e.g., mindfulness training, 11 studies), tertiary (e.g., focused on rehabilitation, 9 studies), and multifocal (e.g., including components of primary and secondary, 9 studies). RESULTS: Tangible changes preceded improvements in health and wellbeing, indicating intervention success cannot be attributed to non-specific factors. Some interventions had beneficial effects through mechanisms not planned as part of the intervention. Three factors were associated with successful WHWP implementation: continuation, learning, and effective governance. CONCLUSIONS: The review indicates future research could focus on how organizations manage conflict between WHWP implementation and existing organizational processes, and the dynamic nature of organizational contexts that affect and are affected by WHWP implementation. This systematic review is registered [PROSPERO: the International Prospective Register of Systematic Reviews ID: CRD42019119656].