The designed landscape was laid out in the early 19th century and the gardens were extended in the late 19th and early 20th centuries.
In early times Ardanaiseig was the embarking point for the holy Isle of Inishail which contains an early Chapel and a burial ground where the 11th Duke of Argyll was buried in 1973 after a funeral ceremony held at Ardanaiseig.
Little is known about the site before 1833 when James Archibald Campbell, a younger son of the Campbells of Inverawe, commissioned William Burn to build the house in the Scottish Baronial style. It was then called New Inverawe but it was written into the deeds of the house that the name had to be changed if it ceased to be a Campbell house. The name was later changed to Ardanaiseig when the house was sold to John Ainsworth.
The Campbell family planted many fine hardwoods, mostly oaks, and various conifers, a few of which still survive, but there is no evidence of any planting by them of decorative shrubs anywhere throughout the policies. Colonel Campbell died in 1879 and in 1880 New Inverawe was sold by his executors to a Mr John Ainsworth from Cumberland, and the name was changed to Ardanaiseig. John Ainsworth became MP for Argyll and was created a baronet in 1916 for his public services. He began the planting of rhododendrons and azaleas along the avenue and near the house, but it was his son, Sir Thomas, who really created the gardens as we know them today when he inherited the property on Sir John's death in 1923.
Sir Thomas lived at Ardanaiseig till shortly after World War II when he decided to move to Ireland and in 1947 the property was sold to Sir Duncan McCallum who was also MP for Argyll. A considerable number of rhododendrons, which were not too old to move, were taken away by Sir Thomas and found a temporary home in Colonsay until his garden in Ireland was ready. This created a time-gap in planting at Ardanaiseig which could never be completely rectified. Sir Duncan died in 1958 and Lady McCallum sold the property in 1963 to the Brown family who are the present owners.
During the years since Sir Thomas Ainsworth went to Ireland the gardens had received little attention but after several years of restoration work it became possible to start new planting and a great deal has been done in recent years to restore the old garden and to open up new areas.
Between 1979-80 the house was converted into an hotel and the grounds are open to hotel guests at all times and to other visitors daily during the summer.