Background: Low- and middle-income countries (LMICs) have limited evidence of adult mortality due to a lack of reliable data. We estimated social (caste and religion) and economic (wealth quintile) inequality in adult mortality using three rounds of the National Family Health Survey (NFHS 1998–1999, NFHS 2015–2016, and NFHS 2019–2021). Methods: We estimated the probability of death in the 15–59 age group by social and economic characteristics. We employed the Cox proportional hazards model to assess the risk of death associated with these characteristics, adjusting for other relevant predictors. Results: Disparities in adult mortality across social and economic groups have persisted for more than two decades, with only marginal reductions in social inequality. In India, the probability of death between ages 15 and 59 (45q15 per 1,000 persons) remains consistently higher among the socially disadvantaged Scheduled Castes (SCs) and Scheduled Tribes (STs) for both men and women. After adjusting for economic factors and regional heterogeneity, Cox proportional hazards models across NFHS rounds indicate that Muslim men have a lower hazard ratio of death than upper-caste Hindu men and that the elevated mortality risk among SCs and STs relative to upper-caste Hindu men is attenuated. Among adult women, upper-caste Hindu women demonstrate the lowest hazard ratios for adult mortality. Higher wealth status is strongly associated with lower mortality risk; individuals from the richest households experience substantially reduced mortality, approximately 60% lower for men and 40% lower for women compared with those from the poorest households across all survey periods. Contribution: This study estimates adult mortality differentials across socioeconomic groups in LMICs using Cox proportional hazards models while accounting for regional heterogeneity.