Before 2000 BC, the apparently indigenous Hattian people established a settlement on sites that had been occupied even earlier and referred to the site as Hattush. The Hattians built their initial settlement on the high ridge of Büyükkale. The earliest traces of settlement on the site are from the sixth millennium BC. In the 19th and 18th centuries BC, merchants from ᴀssur in ᴀssyria established a trading post there, setting up in their own separate quarter of the city. The center of their trade network was located in Kanesh (Neša) (modern Kültepe). Business dealings required record-keeping: the trade network from ᴀssur introduced writing to Hattusa, in the form of cuneiform.

A carbonized layer apparent in excavations attests to the burning and ruin of the city of Hattusa around 1700 BC. The responsible party appears to have been King Anitta from Kussara, who took credit for the act and erected an inscribed curse for good measure:

Whoever after me becomes king resettles Hattusas, let the Stormgod of the Sky strike him!

Only a generation later, a Hitтιтe-speaking king chose the site as his residence and capital. The Hitтιтe language had been gaining speakers at the expense of Hattic for some time. The Hattic Hattush now became the Hitтιтe Hattusa, and the king took the name of Hattusili, the “one from Hattusa”. Hattusili marked the beginning of a non-Hattic-speaking “Hitтιтe” state and of a royal line of Hitтιтe Great Kings, 27 of whom are now known by name.

At its peak, the city covered 1.8 km² and comprised an inner and outer portion, both surrounded by a mᴀssive and still visible course of walls erected during the reign of Suppiluliuma I (circa 1344–1322 BC). The inner city covered an area of some 0.8 km² and was occupied by a citadel with large administrative buildings and temples. The royal residence, or acropolis, was built on a high ridge now known as Büyükkale (Great Fortress).

To the south lay an outer city of about 1 km2, with elaborate gateways decorated with reliefs showing warriors, lions, and sphinxes. Four temples were located here, each set around a porticoed courtyard, together with secular buildings and residential structures. Outside the walls are cemeteries, most of which contain cremation burials. Modern estimates put the population of the city between 40,000 and 50,000 at the peak; in the early period, the inner city housed a third of that number. The dwelling houses that were built with timber and mud bricks have vanished from the site, leaving only the stone-built walls of temples and palaces.

The city was destroyed, together with the Hitтιтe state itself, around 1200 BC, as part of the Bronze Age collapse. Excavations suggest that Hattusa was gradually abandoned over a period of several decades as the Hitтιтe empire disintegrated. The site was subsequently abandoned until 800 BC, when a modest Phrygian settlement appeared in the area.