Consumer demand of minimally processed foods without synthetic preservatives has led to a growing interest in their replacement for more natural alternatives. Onion is widely used as a food ingredient and it is known as a good source of bioactive compounds, such as sulphur-containing compounds and flavonoids with well known health beneficial effects, antioxidant and antimicrobial capacities. Consequently, onion has been proposed as a promising and safer source of food preservatives. The overall aim of the present review is to analyze its potential use as a food ingredient by reporting evidence of onion antioxidant and antimicrobial activities, as well as discussing some concerns in relation to its stability and effectiveness as a food preservative.