The district is located in the southern part of Tamil Nadu. It borders Virudhunagar District to the north, the Western Ghats to the west, Kanyakumari District to the south and Thoothukudi District to the east. The district covers an area of 6,823 km2. It lies between 8°05′ and 9°30′ north latitude and 77°05′ and 78°25′ east longitude.
The district contains mountains (a stretch of the Western Ghats) and lowland plains, including sandy soil and fertile alluvium, and a variety of flora, fauna and protected wildlife. The district also has inland and mountainous forests. Tirunelveli is said to be the only district of Tamil nadu to have all the five types of ecological zones as described in the ancient Tamil Literature Kurunji (hilly), Mullai (Forest), Marutham(Flat fertile land), Neithal ( area forming the seashore) and Palai ( Dry desert lands)
Tirunelveli has rainfall in all seasons (953.1 mm in 2005 and 2006), and benefits from both the northeast and southwest monsoons. Most precipitation came from the northeast monsoon (548.7 mm) followed by the southwest monsoon (147.8 mm) and summer rains (184.2 mm). The district is irrigated by several rivers originating in the Western Ghats, such as the Pachaiyar River, which flows into the perennial Tambaraparani River. The Tambaraparani and Manimuthar Rivers have many dams, with reservoirs providing water for irrigation and power generation. The Tamiraparani River provides consistent irrigation to a large agricultural area. The Chittar River also originates in this district. The Courtallam and Manimuthar waterfalls are the two major falls in the district.