Moral courage is manifested when bystanders intervene to stop or prevent others' norm transgressions, despite potential costs to themselves. Although theoretical models propose a key role of emotions, in particular anger, in the psychological processes underlying moral courage, to date this role is underexplored. In a behavioral study, we proposed a conceptual differentiation between experienced and expressed anger in response to a witnessed moral transgression. By staging the embezzlement of money from project funds in the lab, we tested whether anger arises in response to a witnessed moral norm transgression and scrutinized its unique contribution to predicting who intervenes and who remains inactive in the context of other theoretically relevant emotions (guilt, fear, and empathy). In addition, we investigated the role of bystanders' anger expression in response to the transgression. Lastly, we tested whether experienced and expressed anger reactions were predicted across time from dispositions. Our paradigm allowed us to obtain observational data of behavioral responses and anger expression and experienced emotion reports in response to a realistic moral norm transgression. Results showed that experienced anger increased after the transgression and uniquely predicted intervention. Experienced anger reaction was predictable across time from dispositional sensitivity to observed injustice. Anger expression was only loosely associated with anger experience and intervention, suggesting it may constitute a display of disapproval in itself. The present findings from a realistic moral transgression situation evidence the important role of anger in the psychological process underlying moral courage. (PsycInfo Database Record (c) 2022 APA, all rights reserved).