BACKGROUND: Marijuana use among adolescents, including high school students, has been consistently reported to be associated with a high incidence of suicidal behaviours. Little empirical research has been conducted on the propensity impact of marijuana use on suicidal behaviours in Africa. AIMS: To assess factors associated with marijuana use and further quantify marijuana use as an associated factor of suicidal behaviours, including repeated attempted suicide, suicidal ideation and suicide planning, among high school students in Africa. METHODS: A cross-sectional study was conducted among 32 802 school-going adolescents using the Global School-Based Student Health Survey data from 10 African countries grouped into West Africa, North Africa, South-East Africa, South Africa and East Africa subregions. Marijuana use and repeated attempted suicide were the main outcome variables. We employed double selection least absolute shrinkage and selection operator poisson regression model to assess risk factors associated with marijuana use and dominance analysis to establish ranked important and common risk factors. Inverse probability weighting poisson regression adjustment was applied to assess impact. RESULTS: The prevalence of marijuana use and repeated attempted suicide were 3.7% (95% CI: 3.1 to 4.3) and 6.6% (95% CI: 5.9 to 7.4), respectively. The most important risk factor for marijuana use generally across the countries and specifically in three subregions was alcohol consumption, which constituted approximately 40% of the impact. The average treatment effect on the treated (ATT) indicated that marijuana use significantly increased the risk of suicidal ideation, suicide planning and repeated attempted suicide by 12% (ATT=0.12 (95% CI: 0.02 to 0.22)), 18% (ATT=0.18 (95% CI: 0.13 to 0.22)) and 31% (ATT=0.31 (95% CI: 0.20 to 0.41)), respectively. CONCLUSIONS: Marijuana use was significantly associated with suicidal behaviours (suicidal ideation, planning and repeated attempted suicide) among the students. To achieve Sustainable Development Goal 3.5 (to strengthen prevention and treatment of substance abuse), school-based psychosocial interventions should be streamlined to adequately assess and manage marijuana use. Targeting the most dominant risk factors in this population could translate into the reduction of suicidal behaviours in countries within Africa.