His explorations led to the opening of the Gippsland region for pastoralism, displacing the Gunai Aboriginal people who were the traditional owners of the land.

In 2018, the Australian Electoral Commission announced the Division would be renamed, following a community campaign against honouring a man involved in massacring Gunai people.

After an early life of hardship and deprivation, both in Glen Brittle and subsequently at Kilbride Farm, South Uist, he migrated to Australia in 1838.

[6] Under the initial employ of Captain Lachlan Macalister, he gained experience of Australian pastoralism on the Monaro, New South Wales before moving to manage the Currawang station near Delegate.

The expedition was unsuccessful; in a letter to colonial administrator Charles La Trobe, McMillan reported that six days after leaving Currawong, Gabber declined to go further for fear of encountering the Gunai people, Gippsland's indigenous inhabitants.

[10] No significant agricultural lands or watercourses were discovered along McMillan's path, and neither did he encounter the region's indigenous inhabitants, the Gunai people.

At Macalister's urging McMillan commenced a second expedition in December 1839, moving southwest by west across the plains towards the existing settlement of Sale.

On his return to Currawang in early 1840, he reported to Macalister that he crossed several watercourses draining toward the east, each surrounded by fine potential grazing land.

Increasing European settlement in Gippsland dispossessed the indigenous Gunai people, who were progressively forced off their land to make way for pastoral activities.

[3] McMillan was the source of the White woman of Gippsland rumour, with a letter he wrote to the Sydney Morning Herald on 28 December 1840,[15] which facilitated settler reprisals against the Gunaikurnai people.

McMillan persisted, and, by the 1856 census, he was recorded as the owner of 150,000 acres, upon which he ran the region's second-largest holding of sheep and third-largest of cattle.

In the same year, "Bushy Park" itself was recorded as an eight-room home attached to a four-room cottage, adjacent to a stable, wool store, barn, a worker's hut and a six-acre orchard.

[7] In need of money, in 1864, McMillan acceded to a request from the Victorian Government to lead a team of men into Gippsland's alpine region with the aim of mapping and clearing tracks to support local mining operations.

[7] McMillan's death left his wife and sons destitute, until a public outcry at their plight forced the Victorian Government to come to their aid with a gratuity of £2000.