Child marriage and subsequent early first birth is a considerable social, economic and health concern, and a pervasive practice in sub-Saharan Africa and South Asia. This study explores barriers and facilitators to family planning among women and girls, and their marital decision-makers subsequent to receipt of child marriage prevention programmes in Ethiopia and India. In-depth interviews with 128 women and girls who were married as minors or who cancelled or postponed marriage as minors and their marital decision-makers were analysed using content analysis. Respondents identified social norms, including child marriage and pressure to have children, and lack of information as barriers to family planning. Benefits included delayed first birth and increased birth spacing, improved maternal and child health and girls’ educational attainment. Respondents associated family planning use with delayed pregnancy and increased educational attainment, particularly in Ethiopia. Child marriage prevention programmes were identified as important sources of family planning information. Ethiopia’s school-based programme strengthened access to health workers and contraception more so than India’s community-based programme. Findings highlight young wives’ vulnerability with regard to reproductive control, and support the need for multi-sector approaches across communities, schools and community health workers to improve family planning among young wives.