In June, 1977, Johnson was signed as a free agent by the National Football League's Buffalo Bills.
Appearing in all 16 regular season games, Johnson completed 56.4% of his passes (176 of 312) for 2344 yards, 19 touchdowns, and 8 interceptions as he led the Stampeders to a 12-4 record and a CFL playoff berth.
Granted free agency on January 15, 1983, Johnson returned to the U.S. when he signed with the USFL's Denver Gold five days later.
Facing bitter cold, 20 mph winds, and George Allen's veteran-laden Chicago Blitz squad, Johnson led a 70 yard long game-winning drive late in the 4th quarter.
Johnson would remain the primary starter until an ankle injury ended his season during a Week 11 loss to the Boston Breakers.