Good intentions are important to live a moral life, but they are not enough because people often do not act on them. Indeed, moving from thought to action often requires cognitive resources that can be elusive, in which case we rely on more automatic patterns of thinking and acting. When these automatisms are non-virtuous, individuals may end up acting in harmful ways they later regret (e.g., violence or murder). This study aims to use loving-kindness meditation to lead people to act more compassionately by reinforcing virtuous automatisms. While loving-kindness has been shown to reduce prejudice and increase prosocial behaviour, we do not know whether these effects apply to aggression and whether they remain durable in time. To address these questions, we compare three groups: loving-kindness meditation, loving-kindness discussions, and a wait-list control. We will measure conscious and unconscious aggressiveness, aggressive behaviour, and prosocial behaviour. We hypothesize that after the intervention, both the loving-kindness meditation and discussion groups will show less aggressive and more altruistic behaviour, but only the meditation group should show reduced unconscious aggressiveness. In sum, this project will help develop effective interventions based on loving-kindness meditation to nurture humanity’s social harmony.