Disadvantaged adolescents such as those of low socioeconomic and geographically remote backgrounds experience disproportionate chronic disease burden and tend to engage in greater risk behaviors including poor diet, alcohol use, tobacco smoking, and vaping. The social, structural, and economical barriers to health that uniquely affect adolescents of low socioeconomic and geographically remote backgrounds, such as stigma, access to and affordability of services, may partially explain their disadvantage in attaining health equity. Universal eHealth interventions can provide effective prevention, however, it is unclear whether they benefit disadvantaged adolescents, including those from low socioeconomic and geographically remote contexts. This study systematically reviewed the effectiveness of eHealth interventions targeting disadvantaged adolescents in preventing poor diet, alcohol use, tobacco smoking and vaping. Of 3278 identified records, 15 publications assessing 14 interventions were included, comprising 7170 youth (aged 9–18 years, 50.1% female, 56% low-mid SES, 33% remote). Nine interventions targeted poor diet, three targeted alcohol, one targeted tobacco, and one targeted alcohol and tobacco. No interventions targeted vaping. eHealth interventions significantly increased fruit and vegetable intake and percentage energy of nutrient-rich food, decreased sugar-sweetened beverage consumption, total energy intake, nutrient-poor food percentage energy consumption, and were associated with reduced binge drinking at 1-month follow-up among intervention completers. The findings of this study highlight that eHealth interventions can be effective in targeting poor diet and alcohol use among disadvantaged adolescents. However, due to the limited number of studies meeting inclusion criteria for this study, it is critical future research focus on developing and evaluating effective eHealth interventions targeting disadvantaged adolescents.