Despite a hypothesized link between family conflict and school bullying perpetration, previous findings on the direct association have been inconsistent. It has been argued that affiliation with delinquent peers may be a potential psychosocial mechanism mediating the relationships between family conflict and school perpetration. However, such a proposition has not been examined employing longitudinal panel data. Using longitudinal panel data (two waves with a 9-month interval) from Hong Kong collected from 424 lower secondary students (grades 7–9), this study examined how affiliation with delinquent peers mediates the relationships between family conflict and adolescent school perpetration. The results of the half-longitudinal mediation model indicated no significant link between family conflict at T1 and school bullying perpetration at T2. However, family conflict at T1 was indirectly linked to school bullying perpetration at T2 through affiliation with delinquent peers. The findings imply that affiliation with delinquent peers mediates the association between family conflict and adolescent school bullying perpetration. The findings provide insights into the future development of policies and interventions to reduce school bullying perpetration. Copyright © 2023 The Author(s).