Osgood Mackenzie was the third son of Sir Francis Mackenzie of Gairloch. He was largely educated in Europe. The family estate in Gairloch was inherited by Osgood's oldest brother on the death of their father. Younger sons of lairds were often faced with a choice of joining the military or the church. Osgood took a different path, choosing instead to buy the neighbouring 2,100 acre or (850ha) Inverewe Estate with financial assistance from his mother, which he did in 1862 at the age of 20.
The heart of the estate was a peninsula projecting into Loch Ewe north of Pooloewe. which in Gaelic was called Am Ploc Ard: "the high lump". Despite it being free of any decent soil, completely exposed to every gale sweeping in off the Atlantic, and overrun by rabbits, Mackenzie decided he was going to make use of its one undoubted asset, the warm waters of the Gulf Stream, to create a large garden on the peninsula. Within the entire 50 acre area he had in mind for the garden, there was just one tree, a three foot high dwarf willow. Soil imported from Ireland was carried in by basket, vast numbers of trees were planted for shelter and very, very slowly, Am Ploc Ard became Inverewe Garden, a series of themed gardens home to plants from all round the world linked by a maze of paths. A bare rocky headland was transformed into the Eden that visitors find today.
Osgood Mackenzie continued to work on the garden until his death in 1922, by which time his achievements would have been obvious, and its development was continued by his daughter, Mairi Sawyer. In 1952, a year before her death, she gave Inverewe Garden and an endowment for its future upkeep to the National Trust for Scotland. Today the Garden is one of the most popular attractions for visitors in north west Scotland, receiving around 200,000 visitors each year.