This paper explores the theoretical basis of the third party’s duty of justice as to grave human rights violations, presenting role obligations as the best complement to the literature. It begins with discussions on agents of justice in duty-based theories, notably O’Neill’s account on global justice, and rights-based theories, which are both included in the institution-centred perspective. I claim that these studies have failed to consider an individual duty bearer’s motive, autonomous reasoning and integrity in relation to justice, all of (...) which constitute serious lacunae for the effective accomplishment of responsibility. To supplement, I introduce the distinction between responsibility and commitment, and acknowledge that combining the two is the desirable condition for recognising the duty of justice. Finally, I argue that the role obligations undertaken through personal acceptance of an institution-based role or a commitment-based role related to human rights norms adequately explain third parties’ duty to protect others from serious harm. (shrink)