Russell's Viper grows to a maximum length of 166 cm (centimeters). The average length is about 120 cm on the mainland, although island populations do not attain this size. It is more slenderly built than most other vipers.
The head is flattened, triangular and distinct from the neck. The snout is blunt, rounded and raised. The nostrils are large, in the middle of a large, single nasal scale. The lower edge of the nasal touches the nasorostral. The supranasal has a strong crescent shape and separates the nasal from the nasorostral anteriorly. The rostral is as broad as it is high.
The crown of the head is covered with irregular, strongly fragmented scales. The eyes are large, flecked with yellow or gold, and each is surrounded by 10–15 circumorbital scales. There are 10–12 supralabials, the 4th and 5th of which are significantly larger. The eye is separated from the supralabials by 3–4 rows of suboculars. There are two pairs of chin shields, the front pair of which are notably enlarged. The fangs attain a length of 16 mm in the average specimen.
The body of the snake is stout, the cross-section of which is rounded to cylindrical. The dorsal scales are strongly keeled and only the lower row is smooth. Mid-body, the dorsal scales number 27–33. The ventral scales number 153–180. The anal plate is not divided. The tail is relatively shorter in comparison to the body.
The color pattern of the body of Russell's Viper consists of a deep yellow, tan or brown ground color, with three series of dark brown spots that run the length of its body. Each of these spots has a black ring around it, the outer border of which is intensified with a rim of white or yellow. The dorsal spots, which usually number 23–30, may grow together, while the side spots may break apart. The head has a pair of distinct dark patches, one on each temple, together with a pinkish, salmon or brownish V or X pattern that forms an apex towards the snout. Behind the eye, there is a dark streak, outlined in white, pink or buff. The venter is white, whitish, yellowish or pinkish, often with an irregular scattering of dark spots.