Adolescent girls in Kenya face disproportionately high risk of adverse health and wellbeing outcomes compared to boys. We aimed to evaluate the economic case for investing in a simple package of evidence-based interventions that can be prioritised for improving adolescent girls’ health and wellbeing across Kenya. We combine data collected from published literature into a decision-analytic model to compare the expected cost, impact, and productivity returns of two scenarios between 2024 and 2034. An unchanged policy scenario, and an intervention scenario with progressive scale-up adolescent responsive sexual and reproductive health and rights (SRHR) services, cash transfers, and parenting support. Rates of intervention scale-up were matched to national and regional trends. Modelled outcomes included additional years of schooling; averted child marriage, adolescent pregnancy, HIV infections, emotional, physical and sexual violence victimisation; and expected future productivity returns. Compared to an unchanged policy scenario, our modelled intervention scenario would result in improvements to 2320 primary healthcare facilities, training of 3,740 community health workers, and training of 15,600 peer providers; an additional 333,00 families benefiting from the national cash transfers for orphans and vulnerable children programme; and 122,000 adolescent girls and their caregivers receiving parenting support over the next 10-years. The total cost of the package of interventions was USD 234 million. We estimated that it would avert 120,000 teenage pregnancies, 2660 cases of HIV infection, 5920 cases of child marriage, 8510 experiences of sexual violence, and 54,400 experiences of emotional or physical violence. Furthermore, it would support and additional 226,000 years of schooling, and result in $886 million dollars in future labour market productivity. This package of interventions is also expected to improve adolescent girls’ mental health. However, we were unable to estimate the magnitude of this impact. A complementary package of interventions that together address household economic constraints, access to healthcare, and risk of violence victimisation has impacts across a wide variety of health and wellbeing outcomes with high returns for adolescent girls in Kenya. Investments by governments and development partners in this area are likely to lead to safer, healthier, and more empowered lives.