Continuing progress with preventing smoking initiation is a key to the tobacco endgame. Home- and school-based social networks shape the health behaviour of children and adolescents. This study described the relationship between social connectedness and smoking behaviour in school-aged children in Ireland. The 2014 Irish Health Behaviour in School-aged Children (HBSC) surveyed self-reported smoking status and measured perceptions of social connectedness and support with validated and reliable questions across a random stratified sample of 9623 schoolchildren (aged 10–19). Overall, 8% of school-aged children reported smoking, in the last 30 days 52% reported smoking daily, and prevalence increased with age (p< 0.001). Compared with schoolchildren who did not smoke, perceptions of social connectedness and perceptions of support at home, from peers, and at school were significantly poorer for schoolchildren who smoked across all measures examined (p< 0.001). The poorest rated measures were for school connectedness and teacher support for smokers. Policies and practices that build and support positive environments for schoolchildren must continue to be prioritised if progress on preventing smoking initiation is to be sustained.