Archaeological discoveries on the Leys Castle policies in the 19th century indicate a long settlement history. A late Bronze Age hoard was discovered 'A funicular rod or torc of gold was dug up within the great circle of Leys... in 1824... It measured 22 inches (56cm) long and was hooked at both ends'. The prehistoric Clava-type passage-tomb (SM2417), to the east was named Druidtemple during the 19th century, when antiquarians believed it to be a druidical sanctuary. Previously it was called 'Leys' and late-19th century references refer to 'the great circle of Leys'.
Little is known of the early history of Leys Castle. At the time of Culloden, the Robertsons of Inshes, whose estate lay 3.5km to the north-east, were tenants. Accounts of the indiscriminate slaughter after Culloden mention that a man and his nine year old son, ploughing near Leys Castle, were among the victims (Taylor, 1972). A large house set within parkland existed by the early to mid-18th century when the will of Mr Baillie of Leys (1753) mentions the 'recently planted parkland surrounding the Mansion House.' By 1763, the mansion appears to have been ruined. A number of yew trees estimated to be over 250 years old and an ash of nearly 300 years, may well relate to this 18th century landscape (Saggers, 2001).
By the 19th century Leys estate belonged to Colonel John Baillie (1772-1833). Baillie, the author of The Five Books of Arabic Grammar (1801), had entered the East India Company as a soldier, became a Lieutenant-Colonel and thereafter, between 1801-7, Professor of Arabic, Persian and Mohammedan Law at Fort William College, Calcutta. He served during the Mahratta War (1807-15) as a captain and a political agent in Lucknow. On retirement he became MP for Heddon (1820-30) and thereafter Inverness, 1830-2. He commissioned Samuel Beazley (1786-1851), an architect primarily known for his theatre design, to design the present Leys Castle in 1832-4 (Colvin, 1995). Beazley's castle seems to encase the earlier house (Saggers, personal communication) and is positioned so as to give panoramic views over the parkland. Baillie died before the building was completed.
Although no evidence survives for the involvement of any landscape designer, planting and enclosure records chart the establishment of the designed landscape in the 1820-30s. Survey and analysis of the woodlands confirm this documentation (Saggers, 2001). In 1831, the walled garden, two bridges and Leys Castle Lodge (also known as the Gardener's Cottage) were constructed (Saggers, 2001). The bridges carried estate roads north-eastwards to join the Military Road (which passed between Hilton and Milton of Leys).
Baillie's daughter, married to a relation of John Baillie of Dochfour (see Dochfour, GDL00137) inherited Leys estate. During her tenure the estate was extended westwards by land purchases at Torbreck and Castle Hill. Thereafter, her eldest son, John Baillie Baillie, inherited the estate. He bequeathed his grandfather's collection of Arabic and Persian manuscripts to Edinburgh University in 1876, and lived latterly at Slackbuie. The castle was let to Mr Lawson of Golspie before being sold.
Sometime in the mid to late 19th century a water garden was laid out west of the castle. This led from the Middle Loch, through woodland, to issue down a 4.3m (14ft) deep rocky cascade, into the Lower Pond. This may be contemporary with a formal parterre garden laid out to the east of the castle, which survived until the 1920s (Saggers, 2001).
By the early-20th century the castle was let to the Countess of Southesk (1837-1915), and during the First World War it was used as a Red Cross Hospital. After the war, the estate was occupied by Charles George Ogilvie (1863-1924) (Aberdeen Press and Journal; Find A Grave). Ogilvie is thought to have commissioned George Gordon and Company to re-design the Gardener's Cottage (Leys Castle Lodge) in 1921 and prepare a survey of the house. In 1920, Mrs Ogilvie commissioned Gertrude Jekyll to prepare planting plans for the formal gardens to the east of the castle. Jekyll's plans itemised a complete planting scheme for ten flower borders, including a herbaceous border, a rose garden and planting on the Upper Terrace (NMR England). The scheme was unexecuted and the gardens remained as a series of low hedged, bedding parterres cut into the surrounding lawns (early-19th century photographs; Saggers, 2001).
In 1925, Sir Francis Walker (1873-1963) purchased the estate. An architect, born in Inverurie and articled in Derby, he made a considerable fortune in developing property in Cockfosters and Finsbury in London. A member of Inverness County Council, and Convenor from 1951, he was active in promoting affordable housing in Inverness-shire and the Western Isles in the post-war period and in establishing the publicly-owned Hydro-Electricity Board. He invested in the Leys estate, refurbished the castle, and remodelled the formal gardens between 1926 and 1930. The castle's north facade was radically changed by lowering the ground level, which originally rose above first floor level resulting in the ground floor rooms looking out onto a series of outdoor cellars. The north-west facing sloping ground was remodelled into a series of seven broad terraces. These were symmetrically planted with a collection of specimen conifers, Chamaecyparis, Abies, Taxus, and Sciadopitys. A renowned athlete and swimmer, Walker laid out a swimming pool on the Lower Terrace in 1927 which was fed by the water garden.
In the 1930s, Walker designed and built Leys Home Farm, comprising a modern, 'model' steading for the Leys Castle herd of Highland Cattle. On his death, the estate passed to his son, K.W. Walker, who continued breeding the pedigree Leys fold of Highland cattle. The farm remains in operation (2022).