Crimson rosellas are active and social birds that live in small groups or pairs. They are diurnal, meaning they are active during the day and sleep at night. During the breeding season, male crimson rosellas display elaborate courtship behaviours, including bobbing their heads and displaying their bright plumage to attract a mate. Once a pair has bonded, they will work together to build a nest in a tree hollow, which will line with leaves and bark.

Crimson rosellas are primarily seed-eaters but will also feed on flowers, fruit, and insects. They use their strong beaks to crack open hard seeds and nuts, and their long, agile tongues to extract nectar from flowers. They have been observed feeding on a wide variety of plant species, including eucalyptus, wattle, banksia, and grevillea.