The maroon-tailed parakeet is long and weighs about . The sexes are the same. Adults of the
nominate subspecies P. m. melanura have a mostly green head with a brown crown and nape. Their upperparts are green. Their throat, the sides of their neck, and their breast are dark green with buffy whitish feather edges that give a scaly appearance. The rest of their underparts are green. Their wing is mostly green with red and yellowish orange
primary coverts; their primaries are mostly blue. Their tail's upper surface is maroon with a green base and its under surface is dusky grayish. Their bill is grayish, their iris dark brown with bare white skin surrounding it, and their legs and feet blackish gray. Immature birds are similar to adults but with less red on the primary coverts. Subspecies
P. m. pacifica is darker than the nominate and has no yellow on its primary coverts. Its breast scaling is darker and narrower, its eye ring gray, and its bill blackish.
P. m. chapmani is larger than the nominate with less red on its wing and a red patch on its belly. The scaly appearance of its breast extends around the back of its neck.
P. m. souancei has a more heavily scaled throat than the nominate, with no yellow on the primary coverts, sometimes red on its
carpals, a brownish red belly, and a blacker undertail.
P. m. pacifica has even heavier throat scaling than
souancei, red carpals, and a brownish red belly. ==Distribution and habitat==