Scalloway Castle was built around 1600 for Patrick Stewart, earl of Orkney, who exercised authority over Shetland and Orkney on behalf of the Scottish Crown. The four-story tower house rose beside Scalloway's harbor, then the principal administrative center of Shetland. Its hall, private chambers, kitchens, vaulted rooms, stair towers, gun loops, and formal entrance combined residence, court, storage, and defense. Masonry and skilled labor were drawn from a population already burdened by the earl's rents and demands.

Patrick Stewart's government became notorious for coercive taxation, forced labor, and conflict with local landholders. The castle displayed his rank while providing the setting from which officers administered estates and justice. Heraldic carving and Renaissance detail proclaimed aristocratic authority, but the building's history is inseparable from complaints that island resources were diverted to support the earl's household and construction. Scalloway thus records both elite architectural ambition and the unequal obligations that made such a project possible in a remote maritime region.

The Crown arrested Patrick after investigations into his rule, and he was executed for treason in 1615. His son Robert led a rebellion in Orkney and met the same fate. With the fall of the Stewart earls, the castle passed into royal and official use. Courts and administrative activity continued at Scalloway for a time, but Lerwick's superior harbor and growing trade gradually shifted Shetland's center eastward. Without a resident magnate or sustained institutional household, the tower became increasingly difficult to maintain.

By the eighteenth century the castle was largely roofless, though its walls remained a dominant feature beside the harbor. Travelers and antiquarians recorded the ruin while local memory associated it with oppressive Stewart rule. The building escaped total stone robbing because of its substantial construction and continuing landmark value. Later settlement, roads, and harbor activity changed the immediate setting, but the proximity of sea and administration remained legible in the relationship between the castle, village, and islands beyond.

Modern guardianship stabilized the masonry, stairs, vaults, and carved entrance while keeping the castle as a ruin. Conservation must respond to salt-laden winds, rain, frost, and the vulnerability of high walls without roofs. Scalloway Castle is important not simply as a rare Shetland tower house but as evidence of a contested political system. It connects Renaissance architecture with crown delegation, island labor, judicial power, the fall of the Stewart earls, and the long transfer of Shetland's administrative life from Scalloway to Lerwick.