This bottom-dweller generally inhabits sandy or muddy flats near rocky reefs and kelp forests, to a depth of 30 m (98 ft), though off Hawaii it may range considerably deeper.

As its common name suggests, this species has an angular, diamond-shaped pectoral fin disc that is plain brown or gray above, with rows of tubercles along the midline and on the "shoulders".

The long, whip-like tail has both dorsal and ventral fin folds, which distinguish this ray from the closely similar longtail stingray (H. longa).

It is most active at night and preys mainly on burrowing invertebrates and small bony fishes, which are extracted from the bottom via suction or digging.

Females bear 1–4 pups every summer in estuaries; mating is followed by a ten-month period of either sperm storage or arrested embryonic development, after which the embryos rapidly mature over 2–3 months.

[1] A bottom-dwelling inhabitant of inshore waters, the diamond stingray favors sandy or muddy bottoms, often near rocky reefs or kelp forests.

[1][10] Its pectoral fin disc is rhomboid in shape, slightly wider than long, with angular outer corners and subtly convex margins.

[6][7][11] The whip-like tail generally measures up to one and half times the length of the disc, and bears one (more if replacements have grown in) long, slender, serrated spine on the upper surface, closer to the base than the tip.

This species feeds on crustaceans, molluscs, and other invertebrates, as well as small bony fishes; its powerful jaws and molar-like teeth allow it to crush hard-shelled prey.

[13] In the Bahía Magdalena lagoon complex, Baja California Sur, its most important source of food are pea crabs, followed by the razor clam Solyema valvulus, and then polychaete worms.

[1] Diamond stingrays are frequently trailed by smaller fishes, including Mexican hogfish (Bodianus diplotaenia), Galapagos porgies (Calamus taurinus), greybar grunts (Haemulon sexfasciatum), spinster wrasses (Halichoeres nichols), and long-spine porcupinefish (Diodon holocanthus), which take advantage of the invertebrates stirred up by the ray's activities.

[14] Known parasites of this species include the tapeworms Acanthobothrium bullardi, A. dasi, A. rajivi, and A. soberoni,[15] Anthocephalum currani,[16] Parachristianella tiygonis,[17] and Pseudochristianello elegantissima,[18] the flukes Anaporrhutum euzeti and Probolitrema mexicana,[19][20] and the monogenean Listrocephalos kearni.

Courtship and mating occurs in late summer from July to August, but due to a ten-month period of either sperm storage or diapause (wherein the embryo becomes dormant), embryonic development does not begin until the following year and is completed within 2–3 months.

Elsewhere in its range, it is caught in substantial numbers for human consumption, both intentionally and as bycatch; the pectoral fins or "wings" are sold fresh or filleted and salted.

[6] The International Union for Conservation of Nature (IUCN) notes that the diamond stingray's low reproductive productivity renders it susceptible to population depletion, and assesses it as Vulnerable overall.

[1] In Mexico, the diamond stingray is one of the most important components of Pacific artisanal shark and ray fisheries, comprising around a tenth of the total annual catch.