The Texas alligator lizard is a medium-sized lizard, attaining a maximum total length (including tail) of around 24 to 25 in (61 to 64 cm). It is the largest lizard species in Texas, and one of the largest alligator lizards in the world. This lizard has a flat, wedge-shaped head. Its body is generally a yellow-brown color, often with darker brown and white checker patterning on its dorsal surfaces, and uniformly light-colored, white, or grey on its ventral surfaces. Its scales are very stiff and plate-like. It has short limbs, and a tail that can fall off to distract a potential predator, but will regrow in time.
G. infernalis is often found on rocky hillsides, where it hides among the stones or in limestone crevices.
The Texas alligator lizard is a relatively slow, diurnal lizard, with quite good vision. Though not generally aggressive, it may bite if handled, and is incorrectly considered to be venomous by many cultures.
Breeding occurs year-round; sometimes, multiple clutches of eggs are laid per year. Females will often stay near the nesting site to protect it, but no parental care occurs once the young alligator lizards hatch. The young generally have more striking markings, and are only about 3–4 in (7.6–10.2 cm) long (including tail).