Dianella longifolia is a rhizomatous, perennial herb that forms tufts up to about 1.5 m (4 ft 11 in) tall and has stems less than 10 cm (3.9 in) long.

The leaves are folded lengthwise, grass-like, and 20–80 cm (7.9–31.5 in) long with a rounded to keeled sheath and 2–25 mm (0.079–0.984 in) wide.

The inflorescence is longer than the leaves, the flowers pale blue, white or greenish and well separated from each other, each on a pedicel 7–16 mm (0.28–0.63 in) long.

Flowering occurs in spring and summer and the fruit is a pale blue berry 3–7 mm (0.12–0.28 in) long.

[2][6][7] Dianella longifolia was first described in 1810 by Robert Brown in his Prodromus Florae Novae Hollandiae et Insulae Van Diemen.