The station was opened as Westminster Bridge on 24 December 1868 by the steam-operated District Railway (DR) (now the District line) when the railway opened the first section of its line from South Kensington. It was originally the eastern terminus of the DR and the station cutting ended at a concrete wall buffered by timber sleepers. The approach to the station from the west runs in cut and cover tunnel under the roadway of Broad Sanctuary and diagonally under Parliament Square. In Broad Sanctuary the tunnel is close to Westminster Abbey and St Margaret's church and care was required to avoid undermining their foundations when excavating in the poor ground found there. When the first section of the Jubilee line was planned in the 1970s, the second phase of the project was intended to continue the line eastwards from the terminus at Charing Cross to the City of London, Woolwich and Thamesmead. Westminster station would not have been on this planned route, but the need to provide transport infrastructure for the redevelopment of the London Docklands in east and south-east London led to a redirection of the route to run via Westminster to connect Waterloo and London Bridge stations with the new developments. For the Jubilee Line Extension, the buildings around the station were demolished and the sub-surface station was completely reconstructed together with the erection of a parliamentary office building, Portcullis House, which sits above the station.
The station's architecture is an austere combination of concrete and stainless steel, with stacked banks of escalators supported from the cross-bracing structures spanning the station box and routes for passengers entering or leaving the station separated from those changing between lines. As with the other underground stations on the extension, the Jubilee line platforms feature platform screen doors to improve airflow through the system and increase safety. The station design won a number of awards including Civic Trust awards in 2000 and 2002, the Royal Fine Art Commission Millennium Building of the Year award in 2000 and the RIBA Award for Architecture in 2001. Both projects were jointly short-listed in 2001 for the RIBA's prestigious Stirling Prize. The station is in London fare zone 1. The station has cash machines, Euro cash machines, payphones, wifi, escalators, lifts and boarding ramps.