H. ergaster is sometimes categorized as a subspecies of Homo erectus. It is currently somewhat controversial whether H. ergaster or the later, Asian H. erectus was the direct ancestor of modern humans. The genetic variability among modern Homo sapiens is greatest in Africa, which suggests strongly that this is the area where the species arose and has had most time to accumulate variation. H. ergaster may be distinguished from H. erectus by its thinner skull bones and lack of an obvious sulcus. Derived features include reduced sexual dimorphism; a smaller, more orthognathic face; a smaller dental arcade; and a larger (700 and 850cc) cranial capacity. It is estimated that H. ergaster stood at 1.9m (6ft3) tall with relatively less sexual dimorphism in comparison to earlier hominins. Remains have been found in Tanzania, Ethiopia, Kenya, and South Africa.

The most complete Homo ergaster skeleton ever discovered was made at Lake Turkana, Kenya in 1984. Paleanthropologists Richard Leakey, Kamoya Kimeu and Tim White dubbed the 1.6 million year old specimen as KNM-WT 15000 (nicknamed "Turkana Boy").

The type specimen of H. ergaster is KNM ER 992; the species was named by Groves and Mazak in 1975.

The species name originates from the Greek ergaster meaning "Workman". This name was chosen due to the discovery of various tools such as hand-axes and cleavers near the skeletal remains of H. ergaster. This is one of the reasons that it is sometimes set apart distinctly from other human ancestors. Its use of advanced (rather than simple) tools was unique to this species; H. ergaster tool use belongs to the Acheulean industry. H. ergaster first began using these tools 1.6 million years ago. Charred animal bones in fossil deposits and traces of camps suggest that the species made creative use of fire.