Adolescent pregnancy has important health and social implications. Despite the availability of nationally representative household survey data, there are limited studies that analyze factors associated with adolescent pregnancy across countries of South Asia. This study aimed to identify factors associated with adolescent pregnancy across South Asia. This study used the most recent Demographic and Health Survey (DHS) data from six countries in South Asia: Afghanistan, Bangladesh, India, the Maldives, Nepal, and Pakistan. Pooled individual record data from 20,828 ever-married women aged 15–19 years were used for the analysis. Multivariable logistic regression analysis, informed by the World Health Organization framework on social determinants of health, was performed to examine factors associated with adolescent pregnancy. Adolescent pregnancy was highest in Afghanistan compared to Bangladesh, Nepal, Pakistan, India, and the Maldives. Multivariable analyses confirmed that being from a poor household or male-headed household, increasing maternal age, having no access to newspapers, and having no knowledge of family planning were significantly associated with adolescent pregnancy. The use or intention to use contraceptives was protective against adolescent pregnancy. To reduce adolescent pregnancy in South Asia, interventions targeting adolescents from poor households with limited access to mass media should be considered, especially those from households with an existing patriarchal structure.