Johnstone began singing professionally in Nashville in 1940 on radio and with the dance orchestras of Beasley Smith and Francis Craig.
In 1943 he went to New York City where the following year he was signed by Paul Whiteman for his Philco Hall of Fame radio broadcast on NBC's Blue Network (later ABC).
[1] After service in the United States Merchant Marine in the last 18 months of World War II, he resumed his singing career (changing his name to Johnstone).
In 1946-7, Johnstone sang with the orchestras of Larry Clinton and Harry Soznick, and played an extended engagement at the Copacabana night club as featured singer for headliners such as Frank Sinatra.
Johnstone left Shep Fields' orchestra in Los Angeles in the summer of 1948 and, for family reasons, returned to Nashville.