Lord Garlies redesigned the original formal park in the mid-18th century, influenced by Capability Brown. The grounds and gardens were remodelled c.1850 by the 9th Earl.
It was during the tenure of Alexander, 6th Earl of Galloway (c.1700-1773), that the present house was built between 1740-42 to designs by John Douglas. William Adam had submitted plans but these were amended by Douglas. Sir John Clerk of Pencuik also gave advice and the house was actually built by the master mason, John Baxter. In 1764, Alexander's son, John, 7th Earl (1736- 1806), as Lord Garlies, instructed alterations to the house and began improving the park. He was recognised by contemporary commentators as a 'noted improver' and he is known to have been influenced by 'Capability' Brown's design at Fisherwick in Staffordshire. He wrote that Fisherwick was 'one of the finest parks I ever saw' and when he saw Brown's transplanting machine at work was encouraged to try and move some his trees 'with the greatest care, in a similar way'. In 1791, the Statistical Accounts recorded that Galloway House 'forms part of a landscape truly beautiful and grand' and that the Earl planted over 200,000 trees a year.
Randolph, 9th Earl (1800-1873), planted the ornate parterre in the terrace to the south of the house and began planting the woodland garden in the shelterbelt beyond when he inherited the estate from his father in 1834. He also commissioned William Burn to design further alterations to the house. The 11th Earl was profligate and the extensive estate which covered most of the Machars was sold in 1907 to pay his debts. In 1908, it was sold to the McEacharn family. They engaged Sir Robert Lorimer to remodel the entrance hall and public rooms.
In 1930, the estate was sold again and was bought by Margaret, Lady Forteviot. During World War II the beach at Rigg Bay was the site of the trials for the prototype of the Mulberry Harbour used at the Normandy landings. Between 1947- 53, the house was leased by Glasgow Corporation Education Department.
In 1946 Lady Forteviot's step-grandson, Edward Strutt, inherited the estate and maintained and farmed it until 1958 when the farm buildings and farmland were sold to Messrs T.C. and T. McCreath. Mr Strutt retained 40 acres of parkland and approximately 100 acres of woodland, including the woodland garden and walled garden, which he and Mrs Strutt have permanently opened to the public.
Glasgow Corporation Education Department had a lease on the mansion house from 1947. In 1953 it was sold to Glasgow Corporation who ran it as a Residential School for Glasgwegian children until it was closed for economic reasons in 1976. In 1985 the mansion house and surrounding lawns were bought by Mr and Mrs Wallis from the USA as a private residence.