An adult great spotted woodpecker is 20–24 cm long, weighs 70–98 grams and has a 34–39 cm wingspan. The upperparts are glossy blue-black, with white on the sides of the face and neck. Black lines run from the shoulder to the nape, the base of the bill and about halfway across the breast. There is a large white shoulder patch and the flight feathers are barred with black and white, as is the tail. Males have a crimson patch on the nape, which is absent from the otherwise similar females.

The call of the great spotted woodpecker is a sharp kik, which may be repeated as a wooden rattling krrarraarr if the bird is disturbed. The courtship call, gwig, is mostly given in the display flight. Drumming on dead trees and branches, and sometimes suitable man-made structures.

Great spotted woodpeckers are strongly territorial, typically occupying areas of about 5 ha (12 acres) year-round, which are defended mainly by the male, a behaviour which attracts females. Pairs are monogamous during the breeding period, but often change partners before the next season.