The station was opened on 15 December 1906 by the Great Northern, Piccadilly and Brompton Railway (GNP&BR), the precursor of the Piccadilly line. When the station was rebuilt in 1933 with escalator access to the platforms, a new sub-surface ticket hall was built to the west under the roadway and new station entrances were constructed on the corner of Piccadilly and Stratton Street and on the south side of Piccadilly. The station name was changed at this time. With the rebuilding of the station and similar works at Hyde Park Corner, the little-used Piccadilly line station between the two at Down Street was taken out of use. The Victoria line platforms opened on 7 March 1969; interchange between that line and the Piccadilly line was via the ticket hall (without having to pass through the exit barriers). Even today changing between the Jubilee and Victoria lines and the Piccadilly line involves a long walk. The Jubilee line platforms opened on 1 May 1979, at which time the next station south on the Jubilee line was its then southern terminus, Charing Cross; those platforms were closed when the Jubilee line was extended on a new alignment towards Westminster, during the same time that interchange facilities at Green Park were improved. When travelling south from Green Park on the Jubilee line, Green Park Junction, where the new line diverges from the old, is visible from the train. While passenger services no longer operate to Charing Cross on the Jubilee line, the old line is used regularly to reverse trains when the eastern part of the line is closed due to engineering works.
Work commenced in May 2009 to install two lifts from the ticket hall to the Victoria line platforms and an existing interchange passageway giving access to the Piccadilly and Jubilee lines platforms from the lower lift lobby. This work was completed ahead of schedule in August 2011 when the new lifts were brought into service, along with a third lift between street level on the south side of Piccadilly and the ticket hall. All platforms have level access to the trains, making the station fully accessible (the first one within the Circle line). There is also a new ramp from the ticket hall into the park featuring green walls and a stunning canopy above the staircase and lift on the south side of Piccadilly, the new street structures featuring artwork within the Portland stone cladding designed by John Maine RA. The Diana Fountain was relocated from its original site in the centre of the park to form the centrepiece of the new entrance. There is a unique pattern to the tiles between the Jubilee and Piccadilly line platforms - there are several silver tiles at the Jubilee line end of the tunnel, which are gradually replaced by dark blue tiles at the end of the tunnel with the Piccadilly line platforms. The station has lifts, escalators, cash machines for sterling and euros, wi-fi and payphones.
Connections: Piccadilly and Victoria Lines. London Buses routes 9, 14, 19, 22, 38 and C2 serve the station.
