Venomous snakes are a public health concern in India, where they kill tens of thousands of people annually. Russell's Vipers are the major culprit, but despite their clinical significance, there is virtually no information on their ecology. I used radiotelemetry for a 9-mo period to study the spatial and behavioral ecology of a population of Russell's Vipers (Daboia russelii) in a human-dominated rural landscape in Karnataka, India. Russell's Vipers spent a substantial amount of time in plantations, which make up a significant proportion of the landscape. Snakes were the least active in March, a dry month with the hottest monthly mean maximum temperatures recorded; and spatial activity comparatively increased in late fall-early winter and May, corresponding with the timing of mating activities and the end of the dry season, respectively. Russell's Vipers basked throughout the year, but basking behavior was more frequent in January and February, when the monthly mean minimum temperatures were the lowest. The probability of observing a snake basking increased with decreasing minimum temperatures. Similarly, the snakes were found in ambush foraging postures during daytime throughout the year, and the odds of observing diurnal foraging increased with increasing minimum temperatures and was affected by an interaction between maximum temperature and sex. Overall, the data indicate that this tropical viper actively thermoregulates and is to some extent diurnal. This study provides the first quantitative field-based natural history information on Russell's Vipers, one of the most medically important snakes in the world.