Armstrong was born in Plano, Tex., on Sept. 18, 1971. He entered sports at a young age, excelling in both swimming and cycling. By the time he was a teenager, he was competing in triathlons and swimming competitions. Before his high school graduation, the Junior National Cycling Team, part of the U.S. Cycling Federation, had already recruited him. Armstrong competed in Moscow at the Junior World Championships and in 1990 won the U.S. Amateur Championships. In 1992 he turned professional, joining the Motorola team. One year later he became the second youngest champion in world road racing, and he ranked fifth in world standings. Armstrong won legs of the Tour de France in both 1993 and 1995 but withdrew from three of four Tours he attempted from 1993 to 1996.

After the 1996 Tour de France, Armstrong fell ill, and later that year doctors diagnosed him with testicular cancer, which had by that time also spread to his lungs and brain. He underwent surgery and chemotherapy. Between treatment sessions, Armstrong still took rides of some 30 miles (48 kilometers). By April 1997 the tumors had disappeared.

In September 1997, Armstrong, unranked and riding with the French Cofidis team, finished a respectable fourth in the Tour of Spain. He joined the United States Postal Service team in October and began preparing for the 1999 Tour de France. Armstrong won the opening stage and all three time trials of the 2,254-mile (3,630-kilometer), 22-day race, winning by 7 minutes and 37 seconds.

During the race, traces of a banned substance—corticosteroid from a prescription skin cream Armstrong used for saddle sores—were found in his urine. The International Cycling Union cleared him, but he continued to endure accusations of doping, especially from the French press. Thus, Armstrong believed his win of the 2000 Tour de France was a vindication of his 1999 win and an answer to his critics. He won the 21-stage race 6 minutes and 2 seconds ahead of his nearest competitor. Armstrong won the next two Tour de France races with even stronger showings. He finished the 2001 race 6 minutes and 44 seconds ahead of the next cyclist and the 2002 race with a margin of 7 minutes and 17 seconds.

In 2003 Armstrong claimed his fifth consecutive Tour de France, tying a record set by Miguel Indurain of Spain. Armstrong completed the race in 83 hours 41 minutes 12 seconds, beating runner-up Jan Ullrich of Germany by 61 seconds. In 2004 he won his record-setting sixth consecutive race with a time of 83 hours 36 minutes 2 seconds, which was 6 minutes and 19 seconds faster than that of the second-place rider.

Armstrong established the Lance Armstrong Foundation to provide support for cancer patients and to fund research for testicular cancer, and he made numerous appearances on television. His autobiography, It's Not About the Bike: My Journey Back to Life, was published in 2000.