The station was opened on 24 December 1868 by the District Railway (DR, now the District line) when the company opened the first section of its line between South Kensington and Westminster stations.[8]
The construction of the station was complicated by the crossing of the site by the River Westbourne which ran through Hyde Park as the Serpentine Lake and was originally crossed by the Knight's Bridge at Knightsbridge. The river was carried above the platform in a large iron pipe suspended from girders. This pipe remains in place today.[9]
The DR connected to the Metropolitan Railway (MR, later the Metropolitan line) at South Kensington and, although the two companies were rivals, each company operated its trains over the other's tracks in a joint service known as the "Inner Circle".
From 1 August 1872, the "Middle Circle" service also began operations through Sloane Square running from Moorgate along the MR's tracks on the north side of the Inner Circle to Paddington then over the Hammersmith & City Railway (H&CR) track to Latimer Road then, via a now demolished link, to the West London line to Addison Road and the DR to Mansion House. The service was operated by the Great Western Railway.[11]
On 30 June 1900, the Middle Circle service was withdrawn between Earl's Court and Mansion House.[12] On 31 December 1908, the Outer Circle service was also withdrawn.[12]
In the late 1930s, the station building was rebuilt in the modern style. Escalators were installed between the ticket hall and the platforms in early 1940, making the station the first on the sub-surface network to have escalators.[13] The new station building did not last long as it was mostly destroyed during World War II. A German bomb that fell in November 1940 killed 37 and injured 79 passengers on a train[14][self-published source] in the station and destroyed the ticket hall, escalators and the glazed roof over the tracks.
In 1949, the Metropolitan line operated Inner Circle route was given its own identity on the tube map as the Circle line. By 1951 the station had been rebuilt again in a similar style to the 1930s building. The arched glass roof was not replaced and the current station does not have the light open atmosphere of the original. The office building above the station entrance is a later addition.
The Hole in the Wall pub on the eastbound platform existed from 1868 to 1985.[15]
On 26 December 1973, a terrorist bomb exploded in the telephone kiosk in the booking office. No one was injured.[17][self-published source]
Former Chelsea-Hackney line proposal
Sloane Square was considered as a potential station on the long-proposed Chelsea-Hackney line which has been absorbed into plans for Crossrail 2. The station is no longer on the planned route.[18]