Johnson's first international success was when he won two silver medals at the 1982 Commonwealth Games in Brisbane, Australia. He finished behind Allan Wells of Scotland in the 100 m with a time of 10.05 seconds and was a member of the Canadian 4x100 m relay team. This success was not repeated at the 1983 World Championships in Helsinki, where he was eliminated in the semi-finals, finishing 6th with a time of 10.44.

At the 1984 Summer Olympics in Los Angeles, he did reach the 100m final and won the bronze medal behind Carl Lewis and Sam Graddy with a time of 10.22. He also won a bronze medal with the Canadian 4x100 m relay team of Johnson, Tony Sharpe, Desai Williams, and Sterling Hinds, who ran a time of 38.70. By the end of the 1984 season, Johnson had established himself as Canada's top sprinter, and on August 22 in Zurich, Switzerland, he bettered Williams' Canadian record of 10.17 by running 10.12.

In 1985, after seven consecutive losses, Johnson finally beat Carl Lewis. Other success against Lewis included the 1986 Goodwill Games, where Johnson beat Lewis, running 9.95 for first place, against Lewis' third-place time of 10.06. He broke Houston McTear's seven-year old world record in the 60 metres in 1986, with a time of 6.50 seconds[1]. He also won Commonwealth gold at the 1986 games in Edinburgh, beating a young Linford Christie for the 100 m title with a time of 10.07. Johnson also led the Canadian 4x100 m relay team to gold, and won a bronze in the 200 m.

By the time of the 1987 World Championships, however, Johnson had won his four previous races with Lewis and had established himself as the best 100 m sprinter. At Rome, Johnson confirmed this status by beating Calvin Smith's 100 m world record, by a large margin of 0.1 seconds, with a time of 9.83 seconds.