Dunbeath is likely to have been a defensive site since prehistoric times. It has been suggested that it could be 'Duin Baitte' mentioned in the Annals of Ulster, besieged in AD 680. The 19th century historian W. F. Skene identified Dunbeath as the site of a battle fought by Brude, the Pictish King. While there is little evidence for either corresponding directly to Dunbeath itself, the place-names of the area indicate widespread Norse influence, if not settlement of the area (Morrison, 1996, pp.64-9).
The Castle dates from the medieval period, and was subsequently largely rebuilt and modified. The earliest certain reference to Dunbeath is a charter granting land to John de Barclay in the late 14th century. An early reference to the Castle in the early 15th century indicates that it was the focus of a Kirktown of its own parish.
In the late 16th century, 'Dun Beth', was encircled on its landward side by a moat (Pont, 1654). A description of 1726 mentions that the Castle 'stands upon a rock, the S. point of it is always washen with the sea and some parts of the E. and W. sides of it are also washen therewith.' (Morrison 1996, p.68).
In 1610 George Sinclair sold the lands and barony of Dunbeath to Arthur, Lord Forbes. James VI then granted the Dunbeath Barony, by a charter of 1619, to Alexander, Master of Forbes, son of Arthur, Lord Forbes. The barony lands included the manor, fortalice, pools, lakes, salmon and 'white fish', fishings, woods and forests as well as towns and extensive lands throughout Caithness. Forbes sold the Dunbeath estate to a wealthy merchant, John Sinclair of Geanies, in 1624. The Sinclairs extensively rebuilt the Castle during the early 17th century. Despite being besieged, captured and garrisoned by General Hurry for the Marquis of Montrose in 1650, the castle survived intact.
The structure of the designed landscape had been laid out by the mid 17th century when the formal avenue was established, focussing on the Castle and cutting across a pre-existing field pattern. The Doocot was built so as to terminate the northern end of the avenue and two square enclosures were laid out on either side of the main approach to the north of the Castle, on the site of the existing Walled Gardens (Roy, 1747-55). It was perhaps at this period, that the moat was filled, so as to connect the Castle on its rock promontory with the mainland.
The Sinclair family undertook significant changes to both Castle and landscape in the 1850s and the 1880s. Ground was enclosed along the length, and to either side, of the avenue to provide shelter belts. The Walled Gardens were developed above the cutting and, to the north, tree belts were planted for shelter. On the northeast perimeter of the formal approach, an existing woodland belt was extended and rough quarried ground around the Doocot was planted up.
Drawings of Dunbeath Castle were exhibited by D. & J. Bryce at the Royal Society of Arts in 1881. It was probably John Bryce (d.1922) who was responsible for a new stable court, gate lodge and entrance. He was certainly employed to remodel the Castle in the baronial style in 1907 and further alterations to the designed landscape, particularly the addition of the crenellated parapet wall on the seaward side of the Castle, may date to this period.
During the mid to late 20th century, the ownership of the Castle changed. The Currie family bought the estate in 1946, and sold it to the Sinclair-Blythes in 1965. When the Avery family bought the estate in 1977, they undertook a substantial restoration programme, including a new land drainage system for the southern walled garden. Its earlier subdivisions of eight compartments were re-established with the assistance of the Highland Lilium Nursery. Dunbeath is now owned by the Dunbeath Partnership.