Observational data from the past century show a weakening trend in summer monsoon over the Indian subcontinent. This is possibly attributed to the reduced land–sea contrast resulting from the Indian Ocean warming under the rapid increase of greenhouse gases in the atmosphere. In contrast, speleothem records indicate that the Indian summer monsoon was stronger during the last interglacial (LIG) warm period than it is today. Using climate model simulations, we show that orbital forcing effect during the LIG, as well as related ocean feedbacks, led to warming in the Eurasian continent and cooling in the Indian Ocean basin. This amplified the land–sea contrast in the region and intensified the Indian summer monsoon. Although the LIG is often portrayed as a potential analogue of future climate, our study shows that the Indian monsoon responded differently to the LIG warming period than it does to current climate warming.