Background : Suicidal ideation and anxiety are common among adolescents although their prevalence has predominantly been studied in high income countries. This study estimated the population prevalence of suicidal ideation and anxiety and their correlates with peer support, parent-adolescent relationship, peer victimisation, conflict, isolation and loneliness across a range of low-income, lower-middle-income, upper-middle-income countries and high-income countries (LMIC-HICs). Methods: Data were drawn from the Global School-based Student Health Survey (GSGS) of adolescents aged 12–17 years between 2003 and 2015 in 82 LM-HICs from the six World Health Organization (WHO) regions. We estimated weighted prevalence of suicidal ideation and anxiety by country, region and at a global level. We used multiple binary logistic regression to estimate the adjusted association between adolescent age, sex, socioeconomic status, peer support, parent-adolescent relationship, peer victimisation, conflict, isolation and loneliness with suicidal ideation and anxiety. Findings: The sample comprised of 275,057 adolescents aged 12–17 years (mean age was 14·6 (SD 1·18) years of whom 51·8% were females). The overall pooled prevalence of suicidal ideation and anxiety were 14·0% (95% CI 10·0-17·0%) and 9·0% (7·0-12·0%) respectively. The highest pooled prevalence of suicidal ideation was observed in the Africa Region (21·0%; 20·0-21·0%) and the lowest was in the Asia region (8·0%, 8·0-8·0%). For anxiety, the highest pooled prevalence was observed in Eastern Mediterranean Region (17·0%, 16·0-17·0%) the lowest was in the European Region (4·0%, 4·0-4·0%). Being female, older age, having a lower socioeconomic status and having no close friends were associated with a greater risk of suicidal ideation and anxiety. A higher levels of parental control was positively associated with a greater likelihood of experiencing suicidal ideation (OR: 1·65, 1· 45-1·87) and anxiety (1·53, 1·30-1·80). Parental understanding and monitoring was negatively associated with mental health problems. Similarly, the odds of experiencing suicidal ideation and anxiety were higher among adolescents who had been experiencing peer conflict (1·36, 1·24-1·50; 1·54, 1·40-1·70), peer victimization (1·26, 1·15-1·38; 1·13, 1·02-1·26), peer isolation (1·69, 1·53-1·86; 1·76, 1·61-1·92) and reported loneliness (2· 56, 2·33-2·82; 5·63, 5·21-6·08). Interpretations: Suicidal ideation and anxiety are prevalent among adolescents although there is significant global variation· Reductions in suicidal ideation and anxiety may be facilitated by family and peer-based interventions aimed at increasing social connectedness between adolescents and enhancing parenting skills. Research to inform the factors that influence country and regional level differences in adolescent mental health problems may inform preventative strategies. Funding Statement: The authors stated: None. Declaration of Interests: All authors have no conflict of interest. Ethics Approval Statement: Global School-based Student Health Survey (GSHS) data are publicly available.