Odiham Castle was built on 20 acres (8 ha) of land acquired from the local lord, Robert the Parker, by modifying a bend in the River Whitewater.

In 1215 it was from either Odiham or Windsor that King John rode out to Runnymede, where he met the barons and attached his seal to Magna Carta.

[3] During the same period a second building was constructed over the moat, this time on the south eastern side of the keep, to provide extra living space.

The castle was also involved in the rebellion led by the powerful Despenser family against Roger Mortimer and Queen Isabella of France, the wife of Edward II.

Using the castle as a prison seems to have been common practice during the 13th and 14th centuries; the nearby Manor of Greywell was required to provide guards one night in three.

[8] The most southerly corner of the moat survives in the form of a small overgrown pond on the opposite side of the canal from the rest of the castle.