The stretch of line from Acton Town (then called Mill Hill Park) to Hounslow was opened in 1883 by the Hounslow and Metropolitan Railway. The motivation behind its opening was property speculation in the Spring Grove area of Isleworth and the line passed through open countryside. At the time what we know as Northfields was farm land, so no station was provided and the nearest being at South Ealing and Boston Road (Boston Manor).
The line was a sleepy steam-hauled branch line, which was electrified in June 1905 as part of the modernisation of the Metropolitan District Railway (MDR). By the time a station was provided in April 1908 housing development in Northfields had been underway for some time. In 1911 it was renamed Northfields & Little Ealing. The station was on the opposite side of the road to the current station and at platform level the canopies and fixtures were of a similar style to those that remain at Boston Manor today.
By now the MDR was part of the Underground Group (UG) and the District Line with its many branches was becoming severely taxed in terms of line capacity. So the UG resolved to extend the Piccadilly line from Hammersmith to Acton Town and for the Hounslow and South Harrow services to be transferred to the Piccadilly Line. This was funded by a cheap loan provided in 1929 by the Government for the purpose of alleviating unemployment.
Northfields was chosen as the site of a ‘Car Shed’ which required considerable earth moving. Work started in 1931 and the four tracks from Acton Town to Northfields along with the new Northfields Station, in the handsome ‘Adams, Holden & Pearson’ style on its current site, opened in December 1932. Piccadilly Line trains had reached Hounslow West in February 1932 and took over all services (sharing peak hours with the District) in March 1933. As part of further service changes in October 1964 the last District Line train ran to Hounslow West and the line became exclusively used by the Piccadilly services.