He studied for the medical profession at the university, but ultimately abandoned it, and went to the West Indies, where, after two years, his health broke down, and he returned to Scotland.
In 1840, Johnston left for Port Phillip (Victoria), and started an hotel in Melbourne, where he became a member of the City Council, and ultimately an alderman.
[2] Johnston was elected one of the first representatives of the City of Melbourne in the Legislative Council, then the only chamber, John O'Shanassy and William Westgarth being his colleagues.
Johnston and R. S. Anderson, then Commissioner of Customs, resigned simultaneously in February 1861, and both joined the O'Shanassy Government in the same capacities in Nov. 1861, and held office till the latter Ministry retired in June 1863.
[3] Johnston Street, Collingwood, a major east west arterial road, is named in his memory.