Pteronotus parnellii have tufts of hair sticking out of the sides of their muzzles, hence the name Parnell's moustached bat. Members of this species have long and narrow wings, and their wing aspect ratio is greater than most bats. Both their ears and tragus are narrow and pointed, and they have a furless chin. Their dental formula is i2/2 c1/1 p2/3 m3/3. During their annual moult, which takes place from May to July, their coat turns from a dark brown/blackish colour to a brilliant orange/fulvous. The male is usually slightly larger than the female.