He moved to the colony of Victoria at the age of 21 to work on the gold diggings. He championed the causes of regulation of the mining industry and Separatism of North Queensland as a separate colony. From January 1879 he was member for Townsville and secretary for public works and for mines in the first and second McIlwraith Ministries.
In January 1890 Macrossan became the Colonial Secretary in the Morehead government.
In the first McIlwraith Ministry, Macrossan successfully introduced the first mining regulations in Queensland on his third attempt in 1881. In 1889 Macrossan expanded upon this success by introducing new regulations which included provisions for a system of inspections by representatives of the miners.
After advocating on the issue for many years, in October 1890 Macrossan brought forward a motion to bring about the separation of the north. Then Premier Samuel Griffith moved an amendment that it was desirable to have separate legislative authorities in southern, northern and central Queensland, which was carried.
In February 1890 Macrossan attended the conference on federation held at Melbourne with Griffith, who was then leader of the opposition, and in 1891 he was one of the Queensland representatives to the first Constitutional Convention.
Four weeks after the conference opened he died, on 30 March 1891. Following a funeral at Street Stephen"s Cathedral, Macrossan was buried in Nudgee Cemetery.
Twelve years later he moved to North Queensland where he became well known among the miners in 1873 was elected a member of the Queensland Legislative Assembly for the Kennedy electoral district.