Johnson won four Olympic gold medals and eight World Championships gold medals.He has held the world and Olympic record in the 200 m, 400 m, and 4 x 400 m relay, and the world record in the indoor 400 m. His 200 m time of 19.32 at the 1996 Summer Olympics stood as the record for over 12 years. Johnson is generally considered one of the greatest long sprinters in the history of track and field.

He is the first male athlete in history to win both the 200 meter dash and 400 meter dash events at the same Olympics, a feat he accomplished at the 1996 Summer Olympics in Atlanta. Johnson is also the only man to successfully defend his Olympic title in the 400 m. Aside from his Olympic success Johnson accumulated eight gold medals at World Championships, and is thus tied with Carl Lewis for the most gold medals won by any runner in history.

Johnson was noted for his unique running style. His stiff upright stance and very short steps defied the conventional wisdom stating that a high knee lift was essential for maximum speed. As of 2012, Johnson holds 13 of the top 100 times for the 200 metres and 27 of the top 100 times for the 400 metres. Of those, he holds 14 of the top 25 times for the 400 metres. He broke 44 seconds for the 400 metres twenty-two times, more than twice as many as any other athlete.