Males usually has a longer wingspan and tail length than female shag.

South Georgia shag can reach 2.5–2.9 kg (5.5–6.4 lb).

Two wings are of moderate length and lack the fifth secondary flight feather.

[2] The female lays 2–3 greyish or bluish eggs during the breeding period, which will be incubated by both parents for 28–31 days.

It has formerly been considered a subspecies of the imperial shag (L. atriceps), but it is now usually treated as a full species.