Healthy food outlet accreditation schemes represent an avenue for incentivizing food retailers to promote healthy eating patterns by improving the healthiness of food environments. This systematic review aimed to (i) assess the impact of food outlet-level accreditation schemes on outlet practices and customer purchases and (ii) identify barriers and enablers to scheme implementation. Peer-reviewed and grey literature were systematically searched. Eligible studies related to outlet-level food and beverage accreditation schemes across any food retail setting. Findings were narratively synthesized by retailer type according to (i) scheme characteristics (governance, targeted products, support, and monitoring); (ii) scheme outcomes (rate of uptake, proportion of certified retailers, impact on purchasing, customer perspectives, and retailer perspectives); and (iii) barriers and enablers to implementation. From 21,943 records screened, 48 were included, covering 26 schemes. Most (18) targeted restaurants or convenience stores. Average uptake was 65% of all outlets approached to participate. Implementation of accreditation schemes was associated with healthier customer purchases in convenience stores, schools, and hospitals, but evidence from restaurants was mixed. Enablers of scheme implementation included support for implementation and maintenance, flexible scheme criteria, and motivated retail staff. Healthy food outlet accreditation schemes represent a promising mechanism for engaging retailers to improve the healthiness of food retail environments.