The Douglas Iris grows mainly at lower elevations, below , though it is occasionally found at heights of up to . It is most common in grasslands near the coast; it is regarded as a noxious weed in pastures, because it forms clumps that inhibit other vegetation, and its leaves are bitter and unpalatable to cattle.
This is a typical beardless Iris of subgenus Limniris, series Californicae, growing from a rhizome that is typically under a centimetre in diameter. Its leaves are about wide. It flowers from April to June. Flowers are usually a purplish-blue, though occasionally white or yellow flowers are found. Two or three flowers are found on each stem, which is of variable height, ranging from tall.
Several varieties have been recognised, for example Iris douglasiana var. altissima (Jeps.) and Iris douglasiana var. oregonensis (R. C. Foster), but the species is highly variable and the varieties may not be well enough defined to be of much practical use. The Douglas Iris hybridises freely with several other species; its natural hybrid with I. innominata has been designated as Iris ×thompsonii (R. C. Foster), and the garden hybrid with the same species as Iris ×aureonympha (E. H. English).