It is the successor of the NW sector, originally created as part of the London postal district in 1856.

The boundaries of the area and its numbered districts have changed over time and are the result of the working requirements of Royal Mail.

The postcode area contains large parts of London Boroughs of Barnet, Brent and Camden with small parts of the City of Westminster and those of Ealing, Hammersmith and Fulham, Harrow, Islington and Kensington & Chelsea.

The NW7 district is a projection as far as Hertfordshire's near edge, which it mirrors or emulates briefly near Scratch Wood.

The remainder of northwest Greater London is covered by the HA, UB, part of the EN and a small section of WD.