Johnston was born in Ireland and came to Upper Canada in 1815, moving to Bytown (now Ottawa, Ontario) in 1827.
However, not long afterwards, Johnston was complaining to the Lieutenant Governor that Christie, as a magistrate, was prejudiced against the Irish and favoured Scottish litigants.
Ottawa at this time did not have a police force, and there was an ongoing conflict between the Shiners, composed of Irish labourers, and French-Canadian lumbermen.
Johnston helped promote the interests of his area and lobbied for the selection of Bytown as the provincial capital.
[1] Although he originally considered himself a reformer, Johnston opposed responsible government, because he thought it threatened the independence of the members.
He also opposed Lord Sydenham's policy of seeking a broad base of support in the Legislative Assembly, earning a reputation as a Family Compact Tory.