Tynwald's lower house, known historically as the 24 Keys, met irregularly inside the grim walls of Castle Rushen in Castletown from the sixteenth century onward. In 1710 they moved into Bishop Thomas Wilson's library, and when that building grew dilapidated, they moved again to a dedicated chamber on what became Castletown's Parliament Square in 1821. For most of its history, the Isle of Man's political life had been organized around its medieval southern capital. Then, in 1860, a new lieutenant governor, Francis Pigott Stainsby Conant, chose to live at the Villa Marina in Douglas instead. Douglas was the boom town: ferries, hotels, money. The Keys held one last sitting in Castletown in 1861 and relocated north.

For nearly two decades the House of Keys met in a borrowed courthouse on Atholl Street. In the late 1870s they began looking for something more dignified. The building they wanted was the former Bank of Mona headquarters, designed by John Robinson in the neoclassical style and finished in brick with a whitewash skin. The Bank of Mona had been a subsidiary of the much larger City of Glasgow Bank, which in October 1878 collapsed in a fraud-laced ruin that wiped out shareholders across Scotland and beyond. The Manx subsidiary's grand corner premises sat suddenly empty. The Tynwald acquired the building in December 1879. The old banking hall, with its arcaded ceiling and curved entablature, became the chamber of the House of Keys. The Legislative Council, the revising upper house, settled into a room on the first floor.

Robinson's interior had been built for cash, not legislation, but the bones suited the new use. The ground floor's modillioned cornice ran around the new debating chamber. The sash windows admitted the same north light that had once illuminated bank ledgers. The Tynwald sits on the upper floor in joint session: Keys and Council together, plus the Bishop of Sodor and Man, the Attorney General, and the President of Tynwald. The 125th anniversary of the chamber was marked here in December 2019. It is a working parliament rather than a museum, and visitors walking up Finch Road in session weeks can sometimes see members coming and going through the columned entrance, briefcases in hand.

For a building that hosts a thousand years of self-government, the Legislative Buildings spent a surprisingly long time without formal heritage protection. That changed in September 2025, when the Manx Government added the complex to the protected buildings register as part of a tranche of thirteen newly safeguarded landmarks. The case was straightforward: this is where the world's oldest continuously functioning parliament does its business, in a former Scottish bank, on a wedding-cake corner in a Victorian seaside resort that became a capital almost by accident. Few buildings carry more compressed Manx history per square foot.