The Constable's (or Norman) House was built in the mid to late-12th century in the NE angle of the curtain wall of Christchurch Castle as a chamber block. It is rectangular with gables at the N and S ends, and of 2 storeys. and overloooks on its E side a branch of the River Avon, probably cut as a channel to serve the sanitary needs of the occupants. At the N end a hall sits above an undercroft. The hall has elaborate double-arched, chevron-decorated windows (one in the N wall and two in the E), while in the W wall are two plain round-headed windows. In the E wall was a fireplace.

At the S end of the building was the watergate, and presumably a garderobe emptying into the channel. There was probably a bedchamber in the upper storey. The house is built of large blocks of Purbeck rubble, with Binstead and Freshwater stone dressings, and Purbeck marble used for the shafts of the E windows.

Christchurch Castle was bult by Richard de Redvers on the E side of the burh of Twynham early in the reign of Henry I. This castle was a motte and bailey of earthworks and timber. On his death in 1107, Richard's holdings in Devon and Hampshire passed to his son Baldwin de Redvers (d.1155), who supported Matilda iin the Civil War and was rewarded by her with the Earldom of Devon, probably in 1141. After the middle of the century, one of Baldwin's successors replaced the timber keep with a stone one, and built the Constable's House in the NE angle of the curtain wall.

The castle remained intact until 1651, when it was demolished on Cromwell's orders. The Constable's house remained relatively intact, however.

Pevsner dated the building to the end of the 12thc, while O'Brien prefers 1150-60. Rigold suggests the 1160s, 'late enough for a fully developed circular chimney and early enough for Purbeck Marble (? waste layers from newly-opened quarries) to be used in quantity as rubble.' The trumpet scallop capitals may suggest a date in the 1170s or '80s. The lavish use of Purbeck; that on the E window shafts probably polished originally suggests that this was a building of high status. The suggestion that the southern part of the building may be a few years later (Rigold) remains unproven.