<p>Undernutrition and early childhood mortality have been known to vary geographically. And, these geographical variations could influence the synergistic relationship between undernutrition and early childhood mortality. Thus, a spatially explicit structural equation modelling approach adjusted for the spatial dependence was adopted in the study to estimate the relationship between undernutrition and early childhood mortality using aggregate state-level estimates of variables of interest from the National Family Health Survey 2019–21, National Health Profile 2020, Reserve Bank of India Handbook of Statistics on the Indian States 2019–20, Annual Employment-Unemployment Report 2015–16, and National Sample Survey Organisation 2017–18. As the study used data from different sources, the variables were time-detrended and standardised using Blom’s transformation. Results show that a higher prevalence of chronic and acute undernutrition significantly increases under-five mortality, and having a higher prevalence of underweight significantly increases infant mortality. The risk of infant and under-five mortality attributed to undernutrition was observed to potentially vary by geographical region. Inappropriate management of infant, child and maternal feeding practices and poor household hygiene and sanitation significantly increase the risk of undernutrition. The state’s socioeconomic condition also indirectly influences the risk of undernutrition. And, as the relationship between undernutrition and early childhood mortality varies by region, it is crucial to have region-specific interventions with inter-sectoral coordination in the country’s undernutrition management, which will aid in reducing early childhood mortality.</p>