A cormous, perennial geophyte growing 300-500 mm high. The vertical underground stem (20-25 mm diameter) is globe-shaped and covered in layers of thin papery leaves. Modified underground leaves remain at the base of the stem (cataphylls). Three to five reduced leaves, typically flat and often trailing, cover the stem. A lowermost larger leaf, up to 50 mm long, and shorter upper leaves, usually without a blade, are distinguishable. The erect, unbranched flowering stem is flexed outward below the spike. Flowers are funnel-shaped and deep red-pink, occasionally pale in colour. The lower three tepals are each marked with a characteristic median white band. The spike bears 2-3 (sometimes up to 6) unscented flowers, with a style that arches over shorter stamens bearing yellow anthers. This species flowers during the summer months, mid-February to early April.

Gladiolus carmineus is closely related to G. carneus and was once historically confused with G. stefaniae. Differences between G. carmineus and G. carneus are the flowering time (G. carneus flowers in October-November) and the distinctive open structure of the flower. Gladiolus stefaniae is unlike G. carmineus by having larger, scarlet flowers that are shaped slightly differently and occurs in a different area. Another trait  related to the flowering time of G. carmineus, is that the foliage leaves  are completely dry and dead at flowering time. Gladiolus stephaniae is similar in this regard.