BackgroundContraceptive use can prevent unintended pregnancies, early childbearing, and abortion-related deaths. Despite these benefits, the use of modern contraceptives remains low among adolescent girls and young women (AGYW) in Nepal. To address this gap, the Healthy Transitions Project was implemented in Karnali Province, Nepal from February 2019 to September 2021. This study aimed at measuring the effect of Healthy Transitions’ intervention on improving knowledge and use of modern family planning methods among AGYW in Nepal.MethodsWe used a pre- and post-intervention study design to assess the effect of Healthy Transitions project. A quantitative survey was conducted at baseline and after the first cohort of AGYW had completed the intervention (1 year later). The baseline survey was conducted in 2019 with a cohort of 786 married and unmarried AGYW aged 15–24 years. An end line survey was conducted in 2020 with 565 AGYW who were interviewed at baseline. Data analysis was done using STATA version 15.1. The exact McNemar significance probability value was used to decide the significance of difference between baseline and endline.ResultsThe knowledge and uptake of modern family planning methods have increased in the endline compared to the baseline. AGYW recognised 10 out of the ten modern methods at endline, a significant increase from 7 at baseline (p<0.001). Among AGYW, 99% were aware of sources to obtain family planning methods, compared with 92% at baseline (p< 0.001). The proportion of married AGYW using modern contraceptive methods was significantly higher at the endline 33%, than baseline (26%) (p<0.001).ConclusionOur results show that multilevel demand and supply-side interventions, targeting adolescents and young women, their families, community, and health system helped to improve knowledge and use of modern family planning methods among AGYW. The study suggests that these intervention approaches can be adopted to improve family planning use among adolescents and young women in other similar settings.