Carex bigelowii is an abundant, highly variable, perennial sedge that exhibits different growth forms in different habitats. Plants are found from the lowland to alpine zone in Denali, usually in poorly drained sites on acidic, peaty soil such as bogs, muskeg and tussock tundra. Carex bigelowii can be either caespitose (sometimes forming large tussocks in the lowlands) or rhizomatous and has sharply angled, stiff, scabrous stems 10-40 cm tall. Leaves are mostly basal, flat to revolute and 1.5-4 mm wide. The lowest bract is scale- or leaf-like and shorter than the inflorescence. Plants have male and female flowers in separate spikes, but closely clustered together. Spikes are erect, with usually a single terminal staminate spike and 2-3 lateral pistillate spikes. The pistillate scales are purplish-black to black, equal or shorter than the perigynia and with a blunt or ovate tip, but no awn. Perigynia are green, spotted purple-black or mottled on upper half and with a short beak. Fruits are achenes, elliptic and flattened. Carex microchaeta is superficially similar, but has three stigmas (not two), the pistillate spikes are often peduncled and nodding, and the scales are acute-tipped.

Carex bigelowii is perennial and usually one of the first sedges to flower in the spring in Denali.

Carex bigelowii is monoecious, but male and female flowers are produced in separate spikes. Species in the genus Carex are wind pollinated, but usually also self-pollinate to some degree (Bertin 2007; Friedman and Barrett 2009). Seeds are reportedly still viable after up to 200 years in the soil. This species primarily reproduces vegetatively through spreading rhizomes.

Carex bigelowii occurs in a wide variety of habitats including, dry to wet tundra, bogs, solifluction lobes, marshes, gravels and muskeg. It can grow in rocky to sandy soils to peat.

Wide ranging, usually occurs in poorly-drained wet to moist sites.