In this study, we synthesized findings from qualitative studies to identify the key factors that influence child marriage. We used a meta-ethnographic approach coupled with thematic synthesis. We searched literature from nine databases, which were in English language, covering areas in public health, psychology, and social science between 2008 and 2018. Twelve studies were included in the synthesis. We identified six main themes: human insecurity and conflict; legal issues; family values and circumstances; religious beliefs; individual circumstances, beliefs, and knowledge; and social norms. Our findings highlight the impact of human insecurity and conflict, as well as legal issues. In spite of global progress scaling up legislation against child marriage, the legal framework is insufficiently enforced in many settings. Most of the included studies were from the Middle East, Africa, and South Asia. Studies from other parts of the world such as Latin America and Southeast Asia, which have the highest rates of child marriage, are needed.