This study tested an expanded model of the Theory of Planned Behaviour (TPB) incorporating positive moral attitude and ethical self identity, in the domain of sustainably sourced food. The expanded model variables were included in a path analysis with other food choice motives in order to determine their relative importance. The sample consisted of 137 participants (M = 28, F = 109), recruited online via email and newsletter distribution lists. Participants completed an online questionnaire containing the TPB scales of attitude, subjective norm, perceived behavioural control and intention; measures of positive moral attitude and ethical self identity; and food choice motives taken from the Food Choice Questionnaire incorporating revisions by Lindemann and Väänänen (2000). Results indicated that the expanded TPB model was robust, with positive moral attitude and ethical self identity significantly predicting attitudes towards, and intention to purchase sustainably sourced food. Of the food choice motives, only health and ethical values significantly predicted intention, and health and price predicted attitudes; however, overall the TPB model was more parsimonious. Limitations and implications of these findings are discussed, and future research directions suggested.