After playing college football for St. Mary's College of California and Arizona State, Johnson was selected in the second round of the 1953 NFL Draft by the Steelers, the 18th overall pick. He instead played one season of Canadian football for the Stampeders, in which he won the Jeff Nicklin Memorial Trophy as the league's most valuable player. He then signed with the 49ers, and played left halfback in San Francisco's famed "Million Dollar Backfield". He was traded to Detroit in 1957, and became the team's leading rusher en route to that year's NFL championship, their most recent.