The increasing availability of unhealthy processed food products is linked to rising rates of non-communicable diseases and obesity in low- and middle-income countries. Voluntary actions (VAs) are often adopted in lieu of regulating the composition, production, marketing and sale of unhealthy commodities, but their effectiveness is unclear. This realist review examines VAs adopted by the food and beverage industry in low- and middle-income countries. We developed a conceptual framework and followed a three-stage search to identify literature and VAs and, adhering to the Realist and Meta-narrative Evidence Syntheses: Evolving Standards (RAMESES) guidelines, we produced a synthesized analysis of VAs. VAs, often initiated in response to governments’ efforts to introduce regulations, were difficult to evaluate due to vague language and a lack of enforcement mechanisms. The review found no evidence indicating that VAs are effective in safeguarding public health. Yet their implementation has resulted in weaker responses and policy substitution, and so we suggest that VAs have the potential to negatively influence public health and policy.