Since the 1990s, sustainability of diet has become an increasingly important concern for consumers. However, there is no validated multidimensional measurement of motivation in the choice of foods including a concern for sustainability currently available. In the present study, we developed a questionnaire that measures food choice motives during purchasing, and we tested its psychometric properties. The questionnaire included 104 items divided into four predefined dimensions (environmental, health and well-being, economic and miscellaneous). It was administered to 1000 randomly selected subjects participating in the Nutrinet-Santé cohort study. Among 637 responders, one-third found the questionnaire complex or too long, while one-quarter found it difficult to fill in. Its underlying structure was determined by exploratory factor analysis and then internally validated by confirmatory factor analysis. Reliability was also assessed by internal consistency of selected dimensions and test–retest repeatability. After selecting the most relevant items, first-order analysis highlighted nine main dimensions: labeled ethics and environment, local and traditional production, taste, price, environmental limitations, health, convenience, innovation and absence of contaminants. The model demonstrated excellent internal validity (adjusted goodness of fit index = 0.97; standardized root mean square residuals = 0.07) and satisfactory reliability (internal consistency = 0.96, test–retest repeatability coefficient ranged between 0.31 and 0.68 over a mean 4-week period). This study enabled precise identification of the various dimensions in food choice motives and proposed an original, internally valid tool applicable to large populations for assessing consumer food motivation during purchasing, particularly in terms of sustainability.