He served in the ranks of the 27th Battalion during World War I, and was awarded a Military Medal and recommended for a commission.
Along with Beresford Richards, who had been elected for The Pas earlier in the year, he soon became a prominent figure on the party's left-wing.
Johnson and Richards argued that the CCF should promote friendly relations with the Soviet Union after World War II, and should seek cooperation with other progressive and working-class parties to prevent the Conservatives from returning to power at the federal level.
After Richards made their position public in a speech to the legislature, the provincial CCF council suspended both MLAs from the party.
Unlike Richards, whose motivations in 1945 have been described as "naive and confused"[citation needed], Johnson's personal philosophy had shifted to Marxism by this period.
In 1949, he accused social democratic parties such as the CCF of being traitors to the working-class and of propping up the existing capitalist order.
Johnson later attended the Asia and Pacific Rim Peace Conference in the People's Republic of China in 1952, during the period of the Korean War.