The study aimed to understand the trend of underweight among Scheduled Tribe (ST) non-pregnant adolescent girls in India from 2015 to 2021 and learn how demographic and socio-economic predictors are associated with being underweight among ST non-pregnant adolescent girls aged 15–19 in India. The study is based on the secondary dataset from the third, fourth, and fifth rounds of the National Family Health Survey (2015–16 and 2019–21). The study includes 42,164 ST non-pregnant adolescent girls aged 15–19 in pooled dataset. Bivariate and multivariate logistic regression was applied to analyse the data. The study finds that the underweight among ST non-pregnant adolescent girls has not changed from 2015–16 to 2019–21. The significant predictors of being underweight among ST non-pregnant adolescent girls were girls from Hindu religion (AOR: 1.34, p-value: <0.001), unmarried girls (1.29, <0.001), anaemic girls (1.11, <0.001), and girls from western region (1.86, <0.001) were more likely to be underweight, whereas girls from richest wealth household (0.79, 0.012) and girls having non-vegetarian diet (0.88, <0.001) were less likely to be underweight. The prevalence of underweight among ST adolescent girls in India remains unchanged but there is wide regional variation in the prevalence of underweight. The study suggests the need for strengthening the existing policies and programmes. The study also suggests necessary policy specifically targeting some regions where underweight is high.