In the last decade, reduction in adolescent fertility rates in Indonesia has slowed despite national programmes and policies focused on addressing child marriage. Indonesia currently has the highest number of births to adolescent girls aged 15–19 years in Southeast Asia. There is a need to develop a more nuanced understanding of the drivers of adolescent pregnancy in Indonesia to inform programmes and policies tailored to young people’s needs and priorities. This study explored adolescent girls’ pathways to pregnancy across two provinces (Central Sulawesi and West Java) in Indonesia. We conducted participatory timeline interviews with 79 girls aged 15–21 years from urban, peri-urban, and rural communities and inquired about their relationships and life experiences leading up to pregnancy. We conducted follow-up interviews with 19 selected participants to validate and clarify preliminary findings. We identified six pathways to adolescent pregnancy which were broadly differentiated by the timing of pregnancy relative to marriage. Three pregnancy pathways within marriage were further differentiated by the main motivation for marriage–financial reasons, protecting the girl and family’s reputation, or to progress a romantic relationship. Three pregnancy pathways outside marriage were distinguished by the nature of the sexual relationship preceding pregnancy–consensual sex, unwanted or pressured sex, and forced sex. Drivers of adolescent pregnancy include the acceptability of child marriage and stigma surrounding premarital pregnancy, family and social expectations of pregnancy following marriage, harmful gender-based norms and violence, and lack of sexual and reproductive health information and access to services. Adolescents follow varied pathways to pregnancy in Indonesia. The idealisation and acceptance of child marriage is both a catalyst and outcome of adolescent pregnancy, which is occurring amid stigma surrounding premarital sex and pregnancy, harmful gender-based norms and violence, and barriers to contraceptive access and use. Our findings emphasise that there are many drivers of adolescent pregnancy and different pathways will require intervention approaches that address child marriage alongside other key contributors.