Tritonia nelsonii is an herbaceous, deciduous, perennial plant about 300 to 600 mm tall that grows from an underground storage organ, called a corm. The corm is almost spherical, about 15-30 mm in diameter and is covered with fine-textured fibrous tunics and sometimes has a papery neck. The stem is usually unbranched from the base, but sometimes has 2 branches from near the middle. It produces a loose fan of about 4 to 8 leaves that are simple, narrow, green, sword-shaped and twisted weakly towards the tips. Depending on the growing conditions and maintance, the leaf size varies typically around 100-300 mm long and about 2-4 mm wide. A significant feature of the leaves is that they are obviously marked with lines (striated), and the main vein and 3-4 secondary veins are equally prominent. 

The inflorescence stalk produces a spike of about 5 to 12 reddish orange to vibrant red, funnel-shaped flowers, 10-15 mm long. The throat of the flowers is yellowish and pale and the lower petals each have a yellow spot surrounding a 2-4 mm high yellow peg-like protrusion. The petals are not of the same size. The top petal is usually paler inside and it is slightly hooded over the anthers (male reproductive part of a flower). The flowering period is in late summer (February to March). The fruit is a small capsule that holds a number of seeds inside.