In the 20th century, it was placed in state care as a scheduled monument and opened to the public: it is now one of the most-visited castles in Scotland and received 547,518 visitors in 2019.

The name Urquhart derives from the 7th-century form Airdchartdan, itself a mix of the Old Irish aird (point or promontory) and Old Welsh cardden (thicket or wood).

[5] Speculation that Urquhart may have been the fortress of Bridei son of Maelchon, king of the northern Picts, led Professor Leslie Alcock to undertake excavations in 1983.

[5] Adomnán also relates that during the visit, Columba converted a Pictish nobleman named Emchath, who was on his deathbed, his son Virolec, and their household, at a place called Airdchartdan.

[6] The excavations, supported by radiocarbon dating,[7][8] indicated that the rocky knoll at the south-west corner of the castle had been the site of an extensive fort between the 5th and 11th centuries.

[10][11] Some sources state that William the Lion had a royal castle at Urquhart in the 12th century,[12][13] though Professor Alcock finds no evidence for this.

[14] In the 12th and 13th centuries, the Meic Uilleim (MacWilliams), descendants of Malcolm III, staged a series of rebellions against David I and his successors.

The last of these rebellions was put down in 1229, and to maintain order Alexander II granted Urquhart to his Hostarius (usher or door-ward), Thomas de Lundin.

[17] This time Edward installed as governor Alexander Comyn, brother of John, as the family had sided with the English against Robert Bruce.

After fighting at the Battle of Halidon Hill in 1333, where the Scots were defeated, Lauder returned to hold Urquhart against another threatened English invasion.

[19] Over the next two hundred years, the Great Glen was raided frequently by the MacDonald Lords of the Isles, powerful rulers of a semi-independent kingdom in western Scotland, with a valid claim to the earldom of Ross.

In 1513, following the disaster of Flodden, Sir Donald MacDonald of Lochalsh attempted to gain from the disarray in Scotland by claiming the Lordship of the Isles and occupying Urquhart Castle.

[26] James Grant of Freuchie (d.1553) succeeded his father, and in 1544 became involved with Huntly and Clan Fraser in a feud with the Macdonalds of Clanranald, which culminated in the Battle of the Shirts.

[26] Known as the "Great Raid", this time the MacDonalds succeeded in taking 2,000 cattle, as well as hundreds of other animals, and stripped the castle of its furniture, cannon, and even the gates.

In 1644 a mob of Covenanters (Presbyterian agitators) broke into the castle when Lady Mary Grant was staying, robbing her and turning her out for her adherence to Episcopalianism.

[29] When Oliver Cromwell invaded Scotland in 1650, he disregarded Urquhart in favour of building forts at either end of the Great Glen.

[29] When James VII was deposed in the Revolution of 1688, Ludovic Grant of Freuchie sided with William of Orange and garrisoned the castle with 200 of his own soldiers.

[30] Subsequent plundering of the stonework and other materials for re-use by locals further reduced the ruins, and the Grant Tower partially collapsed following a storm in 1715.

There is considerable room for muster on the inland side, where a "castle-toun" of service buildings would originally have stood, as well as gardens and orchards in the 17th century.

A dry moat, 30 metres (98 ft) across at its widest, defends the landward approach, possibly excavated in the early Middle Ages.

[30] The 16th-century gatehouse is on the inland side of the Nether Bailey and comprises twin D-plan towers flanking an arched entrance passage.

[45] Originally of five storeys, it remains the tallest portion of the castle despite the southern wall collapsing in a storm in the early 18th century.

In the 13th century, the mound became the motte of the original castle built by the Durwards, and the surviving walls represent a "shell keep" (a hollow enclosure) of this date.

[50] To the south of this, opposite the motte, is the base of a doocot (pigeon house) and the scant remains of 13th-century buildings, possibly once a great hall but more recently re-used as a smithy.

The excavations have been criticised for not recording the locations or stratigraphic information, but the collection is of great value, and is now mostly in the care of the National Museum, Edinburgh.