The blackbuck is a moderately sized antelope. It stands up to 74 to 84 cm (29 to 33 in) high at the shoulder; the head-to-body length is nearly 120 cm (47 in).  In the population introduced to Texas, males weigh 20–57 kilograms (44–126 lb), an average of 38 kilograms (84 lb). Females are lighter, weighing 20–33 kilograms (44–73 lb) or 27 kilograms (60 lb) on an average. Sexual dimorphism is prominent, as males are heavier and darker than the females. The long, ringed horns, that resemble corkscrews, are generally present only on males, though females may develop horns as well. They measure 35–75 centimetres (14–30 in), though the maximum horn length recorded in Texas has not exceeded 58 centimetres (23 in). The horns diverge forming a "V"-like shape. In India, horns are longer and more divergent in specimens from the northern and western parts of the country.


The white fur on the chin and around the eyes is in sharp contrast with the black stripes on the face. The coat of males shows two-tone colouration: while the upper parts and outsides of the legs are dark brown to black, the underparts and the insides of the legs are all white. Darkness typically increases as the male ages. On the other hand, females and juveniles are yellowish fawn to tan. In Texas, blackbuck moult in spring, following which the males look notably lighter, though darkness persists on the face and the legs. On the contrary, males will grow darker as the breeding season approaches. Both melanism and albinism have been observed in wild blackbuck. Albino blackbuck are often zoo attractions as in the Indira Gandhi Zoological Park (Andhra Pradesh, India).


Blackbuck bear a close resemblance to gazelles, and are distinguished mainly by the fact that while gazelles are brown in the dorsal parts, blackbuck develop a dark brown or black colour in these parts.