Johnstone was born in Longtown, Cumberland, England, in 1935, and studied English at Durham University (St Chad's College).
[1][2][3] He moved to New Zealand in 1961 after working in Britain and spending three years as a colonial administrator in Northern Rhodesia (now Zambia).
[4][5] In his early career in New Zealand, Johnstone was a teacher at Temuka District High School (now Opihi College), and worked part-time as an announcer at Radio 3XC in Timaru.
[2][4] Johnstone was an interviewer for the weekly television programme, Close Up,[6] and became a reporter and producer for Compass, which aired from 1964 to 1969.
[8] Johnstone's book, Stand and Deliver, giving his personal view of broadcasting in New Zealand, was published in 1998.