Erected shortly after the Norman Conquest, by Roger de Montgomery in 1067, Arundel Castle was to protect the gap that had been carved by the River Arun through the South Downs. A large castle, of traditional motte-and-bailey design, with the motte 70ft (21.2m) high and the baileys extending north and south when originally constructed. The buildings today rest on 12th century foundations and are predominantly from the late 1800s.

Arundel Castle is approached through a late 19th century lower lodge, across a wooden drawbridge and through the Barbican. Original Sussex flintwork on the walls of the south front can still be seen. The inner gateway built during the 11th century, is one of the earliest parts to survive.

During the 12th century, the Keep was constructed of Caen stone. Some of the fireplaces have survived and under the floor in the centre is a storeroom for provisions in case of a siege. The staircase to the wall walk gives magnificent views of the coast, the town, and the Cathedral. Nine feet thick curtain walls were built round the baileys, supported externally by flat buttresses. The arched entrance, ornamented with Norman mouldings was blocked up and replaced by a strong gate-tower built on the curtain wall of the south bailey. The domestic buildings occupied the south end of this bailey. The gate-tower was later heightened and a two-towered barbican added during the 13th century. The main entrance to the castle consists of the Stone Hall and Stairs and dates from the late Nineteenth Century.

After the Civil War, Arundel Castle remained in ruins for some fifty years. Some repairs were carried out from 1716, but major reconstruction work did not commence until 1787, when it was commissioned by the Eleventh Duke of Norfolk. However, even today, marks from the cannonballs fired during the siege of 1643 can be seen on the walls.

One of the most significant aspects of the Duke's work is the library, which is now seen as one of the finest examples of Gothic rooms in the country today. In 1790, he constructed an addition to the courtyard side of The Gallery, which consisted of bed and dressing rooms. These were later refurbished, in anticipation of the visit by Queen Victoria and Prince Albert, and are named 'The Victoria Rooms'.

A further restoration programme was carried out in the latter part of the 19th century, which included rebuilding of the domestic blocks, the Billiard Room (the first part of the castle to form an independent family residence), and restoring the Keep and the Barbican. The Chapel was built in Early English Gothic style with key features similar to those found in Salisbury Cathedral and Canterbury Cathedral.

Originally the private chapel, the Dining Room was created by the Eleventh Duke, and later redesigned for the Fifteenth Duke. The Baron's Hall is a superb example of late Victorian architecture and replaced the smaller octagonal great hall built by the Eleventh Duke. The Baron's Hall was built on the site of the original Medieval Hall.

The last work executed was the North East Gateway, completed in 1906. At the entrance to the gateway, statues of the Howard Lion and the Fitzalan horse can be found. These statues, originally located at the Norfolk suspension bridge, were brought to Arundel Castle in the 1930s when the bridge was demolished.