The Toronto Maple Leafs drafted Johnston in 1965. Johnston had spent the previous two seasons playing for the Johnstown Jets of the EHL and the Tulsa Oilers of the Central Hockey League (CHL). Johnston was traded to the American Hockey League's Springfield Indians for Bruce Gamble.
In 1965, the Toronto Maple Leafs selected Johnston after he spent two seasons with the Johnstown Jets (EHL) and Tulsa Oilers (CHL).  He was then traded to the Springfield Indians of the AHL in exchange for Bruce Gamble.