<p>The food environment is considered a key determinant of population diets. To identify opportunities for action to improve diets and food security, this study aimed to investigate the healthiness of retail food environments in Tonga. A cross-sectional assessment of the availability, placement, price promotion, and marketing of healthy and unhealthy foods in all eight supermarkets, and randomly selected samples of convenience stores (<i>n</i> = 30), small grocery stores (<i>n</i> = 20), and street food stalls (<i>n</i> = 10) was conducted between July and October 2023. We used adapted versions of tools from the International Network for Food and Obesity/NCDs Research, Monitoring and Action Support (INFORMAS). Our study found that far more shelf space in supermarkets and convenience stores was allocated to the unhealthy foods measured (83·9% and 88·2% respectively) in comparison to fruits and vegetables. All unhealthy categories (confectionery, soft drinks, savoury snacks, flavoured instant noodles, ice creams, and ice lollies) that were measured were available in 100% of small grocery stores and 80% of street food stalls sold fried foods. Supermarkets dedicated 52·3% and 95·6% of end-of-aisle and checkout displays to unhealthy foods, while comparable figures for convenience stores were 46·3% and 69·6%, respectively. Price promotions, in-store marketing and product placement in prominent displays all favoured unhealthy foods. Our findings will help identify opportunities to improve diets and food security; form a baseline against which to assess the effectiveness of any changes to retail food environments in Tonga and can act as a comparator for other countries in the Pacific region and elsewhere.</p>