The aim of this study was to examine how different bystander roles in peer victimisation situations relate to moral disengagement, defender self-efficacy, and student-teacher relationship quality. Self-reported survey data were collected from 333 middle and junior high school students (10-15 years of age) from four schools in Sweden. Random intercept model analyses of factor scores revealed that, when witnessing peer victimisation, students high in moral disengagement and low in defender self-efficacy were more inclined to act as reinforcers or outsiders, and that students high in defender self-efficacy and student-teacher relationship quality were more inclined to act as defenders. Furthermore, examining these relationships within and between classes revealed that reinforcer and outsider behaviours were more common among students who, compared to their classmates, were higher in moral disengagement and lower in defender self-efficacy, whereas defending was more common among students who, compared to their classmates, were higher in defender self-efficacy. The results enrich the knowledge of factors related to different bystander behaviours, which has potential implications for prevention and intervention work.