The castle was built in 1202 by William Brewer. It passed to the king in 1233 and in 1245 repairs were ordered to its motte and towers. During the 11th century Second Barons' War against Henry III, Bridgwater was held by the barons against the King.
In the English Civil War the town and the castle were held by the Royalists under Colonel Sir Francis Wyndham. Eventually, with many buildings destroyed in the town, the castle and its valuable contents were surrendered to the Parliamentarians. The castle itself was deliberately destroyed in 1645.
Bridgwater Castle was a substantial structure built in Old Red Sandstone, covering a site of 8 or 9 acres (32,000 to 36,000 m²). A tidal moat, up to wide in places, flowed about along the current streets of Fore Street and Castle Moat, and between Northgate and Chandos Street. Unusually, the main entrance opposite the Cornhill was built with a pair of adjacent gates and drawbridges. In addition to a keep, located at the south-east corner of what is now King Square, documents show that the complex included a dungeon, chapel, stables and a bell tower. Built on the only raised ground in the town, the castle controlled the crossing of the town bridge. A thick portion of the castle wall and water gate can still be seen on West Quay, and the remains of a wall of a building that was probably built within the castle can be viewed in Queen Street. The foundations of the tower forming the north-east corner of the castle are buried beneath Homecastle House.