Twenty-one kilometres in length, the motorway runs from Stanley St in Parnell through the Central Motorway Junction, and west through Central Auckland and West Auckland before continuing northwest and terminating outside of Kumeū at the Brigham Creek Roundabout.

A large part of it forms the middle section of the Western Ring Route.

The first section of the Northwestern Motorway, from Waterview to Te Atatū Peninsula, was finished in 1952.

The section involved bridges over inlets of the Waitematā Harbour, which cut the journey between central Auckland and its airport at Whenuapai by 8 km.

From 2012 to 2016 extra lanes were added between St Lukes and Westgate in preparation for the opening, on 2 July 2017, of the Waterview Connection.