The gardens have developed from the mid 19th century to the present day without any break in maintenance or periods without supervision.
In 1862, Osgood Mackenzie's mother purchased the adjoining estates of Inverewe and Kernsary as a gift for her son. Osgood was 20 years old. The Mackenzies were a local family and owned Tournaig at Gairloch. The Walled Garden was built first and completed by 1864 when the site for the house was chosen because of its proximity to it. Shortly afterwards Mackenzie fenced the Woodland Garden against deer and rabbits and planted the peninsula with Corsican and Scots pine trees to provide shelter. Before he started, only one tree, a willow, grew in the boggy heather covering the rocky promontory.
Mackenzie's famous book 'Gardening in the Western Highlands' was published in 1908. It describes in great detail the making of the garden, how he imported soil to replace the pebble beach in the walled garden, and how the rock under the heather was crazed to allow for some drainage and for the tree roots to gain a foothold. In amongst the pines, Mackenzie planted a few ornamental trees including larch, oak, beech and the more exotic Wellingtonias and silver firs. From about 1880, the poorer specimens in the shelterbelts were removed. In their place, a wide range of exotic trees and shrubs were planted and gradually the garden grew. More and more tender plants were tried and many succeeded. Between 1908 and 1918, the date of Osgood Mackenzie's next account of the garden, he recorded several winters without any frost at all. This gave the more delicate plants a chance to get established.
In 1914 a disastrous fire gutted the original house and many of the records of the garden were destroyed. In 1922, after 60 years of gardening at Inverewe, Osgood Mackenzie died. His daughter, Mairi T. Sawyer, who was a keen and knowledgeable gardener, inherited the garden. In 1936 the present house was built on the site of the original one; some of the redundant stone was used to make the rockery. Mrs Sawyer continued to develop the garden and introduce more plants, many of which came from the plant hunting expeditions of the 1920s. In 1952, a year before she died, Mairi Sawyer presented Inverewe estate, of about 2,100 acres, to the National Trust for Scotland with an endowment for its upkeep. As the guidebook explains, 'It was her wish that the garden should always be a source of pleasure for all those who were willing to travel to this remote corner of the Western Highlands.'
In 1954, the Trust appointed Dr J. M. Cowan as the first Representative of the Trust to oversee the management of the gardens and live in the house. For the next 13 years, Kenny John Urquhart remained as Head Gardener; he retired in 1965, after over 50 years at Inverewe.
From 1964 to 1973, Geoffrey Collins was Head Gardener; he was followed by Richard Fulcher (who retired in 1983). Both these gardeners, with the assistance of the NTS Representatives, continued to expand the range of plants grown at Inverewe and to manage the enormous increase in visitors. In 1952 there were only 3,000 visitors and in 1981 there were over 100,000.