Johnson was troubled by injury in 2000 but still made the final at the 2000 Summer Olympics in Sydney, Australia, just missing out on adding to his medal collection by finishing fourth.

2003 in the Stade de France, saw Johnson win his fourth IAAF World Championships in Athletics 110 m hurdles title when he beat Terrence Trammell into second to overtake the three world championship gold medals that Greg Foster had won at the event.

At the 2004 Summer Olympics he tripped over a hurdle in the 2nd preliminary round and was unable to finish the race and reach the final.

Johnson was trained by Curtis Frye, at the University of South Carolina where he served as a volunteer assistant coach.

Johnson has legally finished 11 races in less than 13 seconds, which was the most all time until Grant Holloway secured 12 on September 6, 2024.