Cyberbullying contributes to poor mental health outcomes and quality of life (QoL), and peer victimisation has been shown to be positively associated with both positive and negative metacognition. Whilst metacognitive beliefs are associated with pathological worry, obsessive–compulsive symptoms, and rumination in depression, research is yet to examine whether metacognitive beliefs influence negative outcomes, such as reduced QoL, associated with experiences of cyberbullying. This study examines whether cybervictimisation, cyberbullying and metacognition play predictive roles in QoL, and if metacognition mediates any association between cybervictimisation, cyberbullying and QoL over time. Participants in the Longitudinal Adolescent Brain Study (LABS), aged 12 years and in grade 7, who had completed up to four assessment time-points (T) were included in this analysis: T1: N = 65; T2: N = 61; T3: N = 56; T4: N = 44. Structural equation modeling revealed significant associations between cyberbullying, cybervictimisation, metacognitive beliefs, and QoL. However, mediation analysis showed that only cognitive confidence acted as a partial mediator between cybervictimisation and QoL. The results suggest those who were more frequently cybervictimised had reduced confidence in their memory, which resulted in lower QoL. In addition, uncontrollability/danger and superstition, punishment, and responsibility were all negatively associated with QoL, indicating that as these metacognitive beliefs increased, QoL decreased. Our findings highlight the detrimental impact that cybervictimisation experiences can have on QoL in young people over time, and that some forms of metacognitive beliefs can also impact QoL. These findings can inform educators and health professionals on the importance of metacognition in regard to QoL over time, particularly in those who experience cybervictimisation.