Edwin Johnstone was born in 1905 in Long River, Prince Edward Island and was raised on the family farm. His education started at Long River School, and continued at Prince of Wales College and Dalhousie University. Johnstone worked as a teacher until 1927, when he accepted a position in Charlottetown with the Pure Milk Company. In 1928 he was employed by the Dominion Life Insurance Company and went on to the prominent position of Provincial Manager. In the 1920s and 1930s, Johnstone also operated a small fox ranch near Charlottetown. He became involved in politics in 1948 and was elected Mayor of the City of Charlottetown in 1958. Johnstone died in 1995 at the age of 90, survived by his wife Lynnie and daughter Jane.

Johnstone was very active in his community. He was a member of Rotary for upwards of fifty years and served as President and District Governor of the organization for several years. He made a significant contribution through fundraising for building the (former) Charlottetown Y.M.C.A. On behalf of the Salvation Army, he fundraised for building Sunset Lodge. In 1962, Johnstone was made an honorary member of the Red Cross Society of Canada