St Stephen's Chapel began as a royal place of worship within the medieval Palace of Westminster. A chapel on the site is recorded in the twelfth century, but Edward I launched an ambitious Gothic rebuilding in 1292. Work continued under his successors. The upper chapel was architecturally complete by 1348, when Edward III established a college of canons to serve it; painting and decoration continued into the 1360s. Its two-storey arrangement placed the Chapel of St Mary Undercroft beneath the splendid upper chamber. Royal worship, richly painted surfaces and court ceremony defined its first centuries.

The Reformation changed the building's purpose. After St Stephen's College was dissolved, Edward VI granted the upper chapel to the House of Commons in 1547. The Commons began using it as a debating chamber in 1548 and remained there until 1834. Members sat on benches facing one another, with the Speaker's chair occupying the position of the former altar. This cramped layout shaped the adversarial arrangement later repeated in the modern Commons Chamber. The room was too small for the full membership, and alterations progressively concealed much of its medieval appearance.

From this chamber MPs argued over taxation, royal authority, religious settlement, war and Britain's expanding empire. Its importance rose during the constitutional conflicts of the seventeenth century and the development of parliamentary government. Sir Christopher Wren's late seventeenth-century alterations helped turn the old chapel into a more recognisable legislative chamber. In the eighteenth century the room heard speakers including Robert Walpole, William Pitt and Charles James Fox. The abolition of the British slave trade passed the Commons here in 1807, and MPs debated the Great Reform Act here in 1832. Prime Minister Spencer Perceval was assassinated in the adjoining lobby in 1812.

The fire of 16 October 1834 destroyed the old Commons chamber and most of the medieval palace. Architect Charles Barry placed St Stephen's Hall on the footprint of the chapel as part of the rebuilt Palace of Westminster. The hall preserves the former room's approximate dimensions, while brass studs in the floor identify where the Speaker's chair and the Table of the House once stood. St Mary Undercroft below survived, though it was damaged and subsequently restored. The hall itself suffered wartime damage and later repairs; it is a successor space, rather than the intact sixteenth- to nineteenth-century debating chamber.

Today visitors enter the parliamentary estate through its managed visitor routes and can encounter St Stephen's Hall on a Palace of Westminster tour, subject to the tour itinerary and parliamentary business. The original chamber's historical role is interpreted through the hall, its markers, Parliament's collections and reconstructions. The site joins the medieval royal palace to the history of representative government, while the distinction between the lost chapel, surviving undercroft and later hall remains essential to understanding what can be seen now.