The adult ashy drongo is mainly dark grey, and the tail is long and deeply forked, There are a number of subspecies varying in the shade of the grey plumage. Some subspecies have white markings on the head. Young birds are dull brownish grey.
It is very dark and almost like the black drongo although this bird is slimmer and has a somewhat longer and less-splayed tail. It is found in more tall forest habitat, has dark grey underside lacking the sheen of black drongo. The iris is crimson and there is no white rictal spot. hey can imitate the calls of other birds and are capable of imitating the whistling notes of a Common Iora.