The 2,202-hectare (5,440-acre) national park is situated approximately 20 kilometres (12 mi) north of the Sydney central business district.

Split into three distinct sections, divided by natural geography, urban development and road infrastructure, the park comprises the valley of Middle Harbour Creek and its tributaries, the slopes along the northern side of Middle Harbour as far as Bantry Bay and part of the catchment of Narrabeen Lakes.

There is considerable evidence of past Aboriginal activity in the area, with over 100 Aboriginal sites recorded to date, including shelters, cave art, rock engravings, middens, grinding grooves and a possible stone arrangement.

[3] Much of the park is bounded by residential development along the ridge tops and it is easily accessible at numerous points by road and water.

[3] The national park is defined by the following boundaries A Dry Sclerophyll Forest, Garigal National Park is home to a wide range of fauna, including birds, snakes and a wide range of native mammals (such as bandicoots, koalas, wallabies).