Cyperus laevigatus is a perennial plant with creeping rhizomes that can be either short or elongated and are covered with brown scales. The stems are culms arranged along the rhizome, which may be widely or closely spaced. The culms are smooth, moderately stout, and trigonous, reaching 10–45 cm heights. The leaves are simple and alternate but are reduced to bladeless sheaths that are 3–30 mm long. The leaf apex is mucronate; the surfaces are green, glaucous, subulate, and convolute. The leaf margins are entire, and the sheaths, numbering 2–3, are brown or dark brown and obliquely truncate at the orifice. The uppermost sheath has a short blade, and stipules are absent. The flowers are arranged in an anthelate inflorescence capitate with 1–12 sessile spikelets. There are two involucral bracts, the longest being culmlike, erect, and 3–8 cm long, much longer than the inflorescence, while the shorter is spreading. The spikelets are pale yellowish brown, lanceolate–oblong, slightly swollen, 7–12 mm long, and about 2 mm wide, with an acute apex. The rachilla is tetragonal and not winged. Glumes are pale yellowish brown, herbaceous, closely spaced, and broadly ovate, measuring 2–2.3 mm long, occasionally showing rusty brown striations, with 3–4 nerves on the dorsally depressed keel. The glume apex is obtuse or mucronulate. The flowers are bisexual (perfect), lacking a corolla, with a superior ovary. The styles are short, and there are two stigmas. The fruit is a grayish brown achene, obovate to ovate, dorsoventrally lenticular or convex–concave, about 1.5 mm long, and punctuate with an obtuse apex.  Each fruit contains one seed with a thin seed coat free from the pericarp, a basal embryo, and an abundant endosperm. It occurs in mud flats, sandy coastal sites, and edges of or within fresh, brackish, and saltwater ponds around 0–10 meters.