The Government of Ireland Act 1920 created Northern Ireland and, with it, the need for a parliament building. The new Parliament initially met in Belfast City Hall, where King George V performed the state opening on 22 June 1921, and in the Presbyterian Church's Assembly College nearby. In 1922, Sir Arnold Thornely of Liverpool won the design competition with plans for a grand domed complex housing all three branches of government -- legislative, executive, and judicial. The plural in the building's official name, "Parliament Buildings," dates from those original ambitions. But the plans proved too expensive. The dome was scrapped. The subsidiary buildings were abandoned. Only the central Parliament Building was constructed, its foundation stone laid on 19 May 1928, and the finished structure opened by the Prince of Wales on 16 November 1932.

What was built, even in reduced form, contained surprises. The Great Hall's gold-plated chandelier had originally hung in Windsor Castle -- a gift from Kaiser Wilhelm II to the British royal family. Removed and stored during the First World War, it was never rehung at Windsor. King George V gave it to Stormont instead, where it still illuminates the Imperial Staircase. The House of Commons chose blue benches rather than Westminster's green, which was considered inappropriate for Belfast. A painting gifted by the Dutch Government depicting King William's entry into Ireland was hung in the chamber, then quietly removed when someone noticed it also showed the Pope, who had blessed William's expedition. The Senate chamber, with its red leather seats and Irish damask linen walls, served as a Royal Air Force operations room during the Second World War. An inscription in the marble balustrade of the press gallery records the RAF's gratitude.

Parliament sat at Stormont until 1972, when the British government prorogued the Northern Ireland Parliament and imposed direct rule. For the next quarter century, the building served as headquarters for the Northern Ireland Civil Service. The short-lived Sunningdale power-sharing executive used it briefly in 1974. A rolling-devolution assembly met between 1982 and 1986. When the Good Friday Agreement brought a new Northern Ireland Assembly in 1998, Sinn Fein suggested building an entirely new parliament, arguing Stormont was too associated with unionist rule. No other party supported the idea. The Assembly moved in and remains. On 3 December 2005, 25,000 mourners gathered in the grounds for footballer George Best's funeral. In 2012, 60,000 people filled the estate for an Orange Order parade marking the centenary of the Ulster Covenant.

A statue of Edward Carson stands at the head of the long drive leading to the building, erected in 1932 while Carson was still alive -- a rare honour. Lord Craigavon's statue occupies the Imperial Staircase landing inside the Great Hall, and Craigavon and his wife are buried in the estate grounds. The building itself became a Grade A Listed structure in 1987. Beyond Parliament Buildings, the Stormont Estate contains Stormont Castle, the seat of the Northern Ireland Executive, and Stormont House, once the official residence of the Speaker. Twenty pairs of cast-iron lamp standards line the approach avenue, each one part of the formal listing. What Thornely originally designed as a complex for all government was reduced to a single building, but that building has proved remarkably durable -- surviving bombs, political suspensions, and a security breach in 2006 when loyalist Michael Stone attempted to enter with pipe bombs, a knife, and an imitation handgun.