There is little understanding of how large mammalian herbivores in Asia partition habitat and forage resources, and vary their diet and habitat selection seasonally in order to coexist. We studied an assemblage of four large herbivores, chital (Axis axis), sambar (Cervus unicolor), gaur (Bos gaurus) and Asian elephant (Elephas maximus), in the seasonal tropical forests of Bandipur and Mudumalai, South India, and tested predictions regarding the species’ seasonal diet browse : graze ratios, habitat selection and habitat-niche preference and overlap. Field data collected for the study included the seasonal variation in grass quality, the seasonal variation in d13C in the species’ faeces and the seasonal variation in the species’ habitat selection and overlap using a grid-based survey. Results of the d13C analyses showed that the chital was more of a grazer in the wet season (-17.9‰to -21.6‰), but that it increased the proportion of browse in its diet in the dry season (-25.6‰ to -27.7‰); the gaur was a grazer for most of the year (-15.3‰to -18.6‰); the sambar preferred to browse throughout the year (-21.1‰to -30.4‰); and that the elephant was a mixed feeder (-14.2‰to -21.4‰). Elephant habitat-niche breadth was high (0.53 in wet and 0.54 in dry) and overlapped equally with that of the other species in both seasons (0.39–0.94). The gaur had the most restricted habitat-niche breadth in both seasons (0.25 in wet and 0.28 in dry), and it switched from the moist deciduous habitat in the dry season to the dry deciduous habitat in the wet season. These results offer the first insights into the seasonal variation in browse : graze diet ratios and the habitat-niche overlap amongst the common largest-bodied mammalian herbivore species found in South India.