The Western Diamondback Rattlesnake is generally colored a shade of dark or light brown. Its pattern is a distinctive row of large, dark diamond shapes edged in yellow trim, running down the length of its body. The diamonds fade to dark rings around the tail, where the distinctive rattle begins. A dark stripe edged in yellow runs back from the mouth to the eyes on each side of the head. There is no significant difference in appearance between males and females except that males are generally larger. They grow to an average length of 4½ feet, but can reach a maximum length 6½ feet.

Though large and bulky in appearance, the Western Diamondback can strike up to two-thirds of its body length. That's about a three to four foot striking range for larger specimens. It strikes with two large, hollow fangs which inject venom into its prey eventually killing it (venom is lethal to small animals within minutes). The fangs are retractable and replaceable as venomous snakes lose and replace fangs often. The snake's movement is in a rectilinear fashion (unlike sidewinders).

Western Diamondbacks can live for more than twenty years, but life expectancy is typically shorter because of hunting and human expansion. Solitary outside of mating season, they are one of the more aggressive species found in North America because they rarely back away from confrontation. When threatened they usually coil and shake their rattle to warn aggressors that they have stumbled upon something dangerous.

The Western Diamondback, like other desert snakes, can go for up to two years without food in the wild.

The snake is a poor climber and primarily hunts small mammals, but will also feed on birds, small reptiles and amphibians. They hunt (or ambush prey) at night or early morning using a type of infrared sense prominently found in pit vipers. Although adult specimens have no natural predators, hawks, eagles, and other snakes can prey on young or adolescent individuals.