Some shadar-kai resembled blighted elves, in a perpetual state between life and death, while others were human-like in appearance. They were usually slender and ranged from slightly taller to slightly shorter than humans, exhibiting graceful movements well suited to stealth.

They had dusky gray skin and colorless complexions that varied from alabaster to dark gray; black hair, with few shadar-kai having pale hair, that ranged within human hair colors; and dark eyes lacking any sclera or clear pupil. Shadows on their bodies or clothing always seemed to be deeper and darker than shadows elsewhere, and shadow seemed to follow them and reach out, especially when they were angry. They were easily lost from view. Many shadar-kai displayed all kinds of iron body piercings in nose, ears, eyebrows, shoulders, and other parts of the body, and purple-inked tattoos on body, limbs, and face.

Despite having a somewhat youthful appearance while in the Material plane, being in the Shadowfell revealed the shadar-kai's cursed state to those who had made a deal or taken the mark of the Raven Queen: They appeared visibly aged and withered, with swollen joints that gave them an overall corpse-like aspect. For that reason, many shadar-kai wore masks to conceal their decrepit state while in the Shadowfell.

Shadar-kai bred true. Their pairings produced shadar-kai offspring, as well as the pairing between a human and a shadar-kai.