The plant has hairy, dark green, broadly oval rosette leaves to 30 cm long. The several seeding stems grow to 120 cm in height and develop branches with age. Flowers develop in clusters; they are purple, tubular and 2–3 cm long with 5 petals. It has a fleshy taproot with smaller laterals.
Although generally an autumn germinating spring-flowering annual, Paterson's Curse has become highly adaptable to Australian erratic rainfall events and, given suitable rainfall, some plants germinate at any time of year, but the plant never survives for more than one year. It is a very prolific seed producer; heavy infestations can yield up to 30 000 seeds per square metre. Paterson's Curse can germinate under a wide variety of temperature conditions, tolerates dry periods well and responds vigorously to fertiliser. If cut by a lawnmower, it quickly recovers and sends out new shoots and flowers.
The plant disperses by movement of seeds — on the wool or fur of animals, the alimentary tracts of grazing animals or birds, movement in water and most importantly as a contaminant of hay or grain. This is most noticeable in times of drought, when there is considerable movement of fodder and livestock.
It can rapidly establish a large population on disturbed ground and competes vigorously with both smaller plants and the seedlings of regenerating overstorey species. Its spread has been greatly aided by human-induced habitat degradation, particularly the removal of perennial grasses through overgrazing by sheep and cattle and the introduction of the rabbit. Paterson's Curse is rarely able to establish itself in habitats where the native vegetation is healthy and undisturbed.