Adolescent loneliness is prevalent and poses a significant risk for youth mental health. This study aimed to estimate the global prevalence and distribution of frequent perceived loneliness in adolescents and its associations with suicidal ideation, planning, and attempts. We analyzed data from the Global School-based Student Health Survey (GSHS) across 93 countries/territories (2003-2021) for adolescents aged 11-18. Weighted prevalence of frequent perceived loneliness was estimated for each country/territory, with pooled prevalence calculated by sex, age, WHO regions, and economic groups. Binary logistic regressions were employed to assess the associations between loneliness perception and suicidal behaviors in each country/territory, with overall estimates derived by random-effects meta-analysis. Among 388,093 adolescents included, 13.2% (95% CI 12.2-14.3%) reported frequent perceived loneliness, with the lowest observed in Europe (North Macedonia and Tajikistan) at 4.6% (95% CI 1.1-8.1%) and the highest in the Eastern Mediterranean at 16.1% (95% CI 14.7-17.6%). Girls and older adolescents had higher prevalence of frequent perceived loneliness. Frequent perceived loneliness was significantly associated with increased odds of suicidal ideation (overall OR: 2.41, 95% CI 2.25-2.58), planning (overall OR: 2.06, 95% CI 1.92-2.21), and attempts (overall OR: 2.08, 95% CI 1.95-2.20). These associations were consistent across most countries/territories, sexes, age, regions, and economic groups. These findings highlight frequent perceived loneliness in adolescents as a global public health concern strongly linked to suicidal behaviors, underscoring the urgent need for targeted interventions to address loneliness and its mental health consequences.