Ethical consumption has become an increasing trend as young customers get increasingly aware of their environmental and ethical responsibilities. The study aimed to examine the determinants of organic food purchase intention and behaviour of young customers in South Africa by extending the Theory of Planned Behaviour (TPB). The main objective of the study was to determine the effects of TPB constructs (attitude, subjective norms and perceived behavioural control) on young consumers’ intention to purchase organic food. Also, the study investigated whether the extended TPB model would improve the predictive validity of the model. The TPB was modified by the addition of three value constructs (health, environmental and appearance consciousness) as antecedents of attitude and intention and two personal factors (moral norms and ethical self-identity) as predictors of purchase intention. In addition, the study examined the mediating effects of attitude towards organic food in the relationship between value and purchase intention. Furthermore, the study determined the effect of intention on actual organic food purchase behaviour of young consumers. The study adopted a quantitative research approach and data was collected through the cross-sectional survey method using self-administered questionnaires from four hundred and three respondents. The questionnaires were distributed to the respondents through mall intercept and the Partial Least Square Structural Equation Modelling (PLS SEM) was used to test the hypotheses of the study. The findings confirmed that two constructs of the TPB (attitude towards organic food and perceived behavioural control) are predictors of purchase intention. In addition, health and environmental consciousness are antecedents of attitude and intention. Attitude mediates the relationship between health, environmental consciousness and intention. Furthermore, intention is a predictor of behaviour. Recommendations to improve the purchase of organic food focus on communication by marketers to consumers about the benefits of organic food. The study concludes that the extended TPB is an applicable theoretical framework to explain the purchase of organic food by young consumers.