It has a total area of 4000 km², and lies between the Auckland Region, the Coromandel Peninsula, and the Hauraki Plains. Hauraki is Māori for North Wind.

The gulf is part of the Pacific Ocean, which it joins to the north and east. It is largely protected from the Pacific by Great Barrier Island and Hauturu/Little Barrier Island to the north, and by the 80-kilometre-long Coromandel Peninsula to the east. The gulf is thus well-protected against all but northern winds.

Numerous beaches dot the shores of the gulf, many of them well-known for swimming and surfing.

During the last glaciation period the whole gulf was dry land, with the sea level being around 100 m (300 ft) lower than at present.