Background: Early marriage among girls under 19 years remains a significant public health and social concern in the Sundarbans of West Bengal, India. Despite legal restrictions, the practice continues due to socio-cultural norms, economic constraints, and gender inequality. Objectives: To assess the sociodemographic characteristics of girls married before the age of 19 years and to explore their opinions regarding early marriage. Methods: A mixed-methods study employing a convergent parallel design was conducted among 20 girls married before the age of 19 years. Quantitative sociodemographic data were analyzed descriptively, while qualitative insights were generated through two Focus Group Discussions (FGDs) and analyzed using thematic analysis. The findings were integrated using a joint analysis approach to examine convergence, divergence, and complementarity across data strands. Results: Quantitative findings: Most participants were aged 16–18 years (80%), with 90% living with their husbands. A majority were housewives (60%), while others were engaged in daily work or farming. Half had secondary education (50%), while 15% had no formal education. Most participants had no children (65%). Qualitative findings: Early marriage was socially accepted and influenced by family pressure and limited autonomy. Although participants preferred marriage after valued education, early marriage often resulted in school discontinuation. Girls reported a lack of readiness for marital responsibilities and economic dependency. However, many expressed a desire to delay marriage and continue education. Conclusion: Early marriage persists due to entrenched socio-cultural and economic factors despite awareness of its adverse effects. Strengthening education, empowerment, and community awareness is essential to delay the age of marriage.