‘Food sustainability’ is now acknowledged as integral to the achievement of food security, a healthy community and protection of the environment. Understanding consumers’ knowledge of and attitudes towards food sustainability is poorly understood in Ireland. This study aimed to explore the knowledge and attitudes towards food sustainability among visitors to an Irish restaurant, known to prepare foods in a sustainable way. A cross-sectional study was conducted on 426 visitors at the Overends Kitchen, Airfield Estate, Dublin, Ireland using a short questionnaire informed by previously collected data on Irish consumers’ attitudes towards food purchasing and a Department for Environment, Food and Rural Affairs (UK) questionnaire. Information on demographics, food choice motives, food preferences, basic nutritional knowledge, awareness and attitudes toward food sustainability was obtained. Data were analysed using the Statistical Package for Social Science (IBM, v23, Chicago, Ill, USA). Quality (98%) and health (92%) were the most important motives for food choice. Females (P = 0.001) and older (P = 0.029) participants had greater interest in health as a motivating factor for food choice compared to males and those who were younger. Free-range (eggs) and fresh vegetables and fish were most frequently purchased. Poor knowledge of recommendations about saturated fat, and daily fruit and vegetables intakes was demonstrated though this was better in female (P = 0.005) and younger (P = 0.007) participants. Participants demonstrated positive attitudes towards food sustainability and over half (57%) were aware of GLAS principles (Go with the seasons, Local for produce, Avoid food waste, Sustainably produced) although only 37% reported that these principles influence their dietary choices. Misinformation about the environmental sustainability and nutritional value of farmed vs. organic or wild fish and fresh vs. frozen vegetables was apparent. This research provides some understanding of Irish consumers' knowledge and attitudes towards food sustainability. The need to enhance understanding of how diets can be made more sustainable is clear.