Donnington Castle is sited at the top of a hill overlooking the River Lambourne, a mile north of Newbury. A licence to crenellate his property was granted to Sir Richard Abberbury in 1386. The castle was a rectangular enclosure with a round tower at each corner and two square towers midway along the longest sides. The most impressive part of the castle, and indeed the only part now standing, was the gatehouse. This is a three-storey rectangular building with two round towers that flank the entrance and rise another storey above the rest of the building.

During the Civil War the castle was seized by Royalist forces after the first Battle of Newbury. Colonel John Boys was put in charge of its defence and he constructed a series of earthworks in the shape of a star around the castle. They successfully withstood a Parliamentary siege in July 1644. In October, King Charles marched to the relief of the castle, and the second Battle of Newbury was fought around it. This time the King's men were forced to withdraw, but Colonel John Boys refused to surrender the castle. After an eighteen month siege, the garrison finally accepted terms for an honourable surrender and were allowed to march out of the castle and join Royalist forces in Wallingford. The Civil War earthworks still remain around the castle.