South Harrow station was opened on 28 June 1903 by the District Railway (DR, now the District line) as the terminus of its new extension from Park Royal & Twyford Abbey. This new extension was, together with the existing tracks back to Acton Town, the first section of the Underground's surface lines to be electrified and operate electric instead of steam trains. The Deep level tube lines open at that time (City & South London Railway, Waterloo & City Railway and Central London Railway) had been electrically powered from the start. On 1 March 1910, the DR was extended north to meet the Metropolitan Railway (MR, now the Metropolitan line) tracks at Rayners Lane and services commenced over the MR's tracks to Uxbridge. North of the station the line crosses the Roxeth Marsh; the viaduct over it between South Harrow and Rayners Lane was an engineering feat of the time. On 4 July 1932, the Piccadilly line was extended to run west of its original terminus at Hammersmith sharing the route with the District line to Ealing Common.
The original station building was located approximately 170m south of the existing station and was accessed from South Hill Avenue. It is similar to the building still in use at North Ealing and remains, adjacent to the eastbound platform, in the car park on the north side of the tracks. On 5 July 1935, a new station was opened accessed from Northolt Road. The new station building was designed by Charles Holden as a graduated structure stepping up on each side to the platforms of the high level tracks. The brick walls and bands of horizontal glazing are capped with a series of flat concrete slab roofs. It is located on Northolt Road (A312). The station is in Travelcard Zone 5. There is a bus stand outside the station. The station has cash machines, Euro cash machines, payphones, a waiting room, bridge, toilets and car park.
Connections: London Buses routes 114, 140, 258, 395, 398, 487, H9, H10 and H12 serve the station.