Norwich Castle began soon after the Norman Conquest as a royal fortress imposed above one of England's largest towns. William the Conqueror ordered an earth-and-timber castle around 1067, and construction displaced part of the existing settlement. During the Revolt of the Earls in 1075, the garrison held the stronghold for the king. The vast motte and enclosed baileys asserted control over East Anglia, while the castle's royal officers administered estates, justice, taxation, and military obligations from a site that dominated the townscape.

The timber defenses were replaced by a monumental stone keep, begun around the end of the eleventh century and completed under Henry I in the early twelfth. Its richly decorated exterior, great hall, chapel, chambers, service rooms, and galleries made it a palace as well as a fortress. The keep's scale was intended to display royal power. Kings visited less often as the medieval period progressed, but sheriffs and other officials continued to use the precinct for county government and the custody of prisoners.

By the fourteenth century the castle's principal role was judicial and penal. The county gaol occupied the site for centuries, with prisoners held in and around the Norman keep. Buildings were repeatedly added, demolished, and reorganized as ideas about punishment changed. Public executions occurred nearby, while debtors, accused criminals, convicted prisoners, staff, and visitors inhabited a crowded institutional complex. In the early nineteenth century the keep's deteriorated exterior was refaced in stone, preserving its Romanesque appearance but replacing much weathered medieval surface.

A new prison complex transformed the summit in the eighteenth and nineteenth centuries, but the gaol eventually closed in 1887. Norfolk authorities then converted the castle into a museum, which opened in 1894. Galleries of archaeology, natural history, art, and local collections occupied spaces once used for confinement. This adaptation saved the keep while also introducing floors, displays, circulation routes, and services that changed how its interior was understood. Archaeological work later recovered evidence of Norman, medieval, and prison phases beneath the museum buildings.

A major twenty-first-century project has reinterpreted the keep as a Norman royal palace, restoring an internal floor level and improving access while retaining its museum role. The work draws on comparative architecture and archaeology because much of the original interior was lost during centuries of prison use. Norwich Castle now presents conquest, monarchy, law, incarceration, collecting, and conservation within one structure. Its apparently uniform stone exterior conceals a complicated history in which the same commanding hill served successive systems of royal control, county punishment, civic education, and public heritage.