Johnston was born in Enderby, British Columbia and grew up on a farm in the Okanagan Valley.
He studied English and History at university and became a high school teacher.
He was first elected in 1965 under the Social Credit Party of Canada in the Okanagan—Revelstoke electoral district, serving in the 27th Canadian Parliament.
He made another unsuccessful attempt to gain the riding in the 1972 federal election, this time switching to the Progressive Conservative Party.
[1][permanent dead link] Johnston took up painting after retiring from politics.