Prior to her professional cycling career, Armstrong had been a junior Olympian in swimming, a distance runner in college, and then became a triathlete. She spent many hours perfecting her strokes in the pool at the Boise Family YMCA, where she also served as Director of Aquatics, managing more than 50 lifeguards, swim instructors, and others. She was diagnosed with osteoarthritis in both hips in 2001 at age 27, and told that she could no longer run at an elite level, thus ending her triathlon career and leading her to focus exclusively on cycling.
The three-time national champion finished 8th (top U.S. finisher) in the women's road race at the 2004 Summer Olympics in Athens.
At the 2008 Summer Olympics in China, Armstrong completed the biggest achievement of her career by winning the gold medal in the women's road time trial competition on August 13. Finishing in under 35 minutes, Armstrong was 25 seconds ahead of silver medalist Emma Pooley from Great Britain, with Karin Thürig from Switzerland taking the bronze.
Of Armstrong, Velonews wrote: "Kristin Armstrong is famous for both her success in bicycle racing, and the 'type-A' attention to detail that keeps her climbing the podium at critical races every season."
Armstrong announced at the end of 2010 that she would return to competitive cycling, with the goal of competing in the 2012 Summer Olympic Games in London. In a written statement, she stated that her retirement was merely temporary in order to start a family. "I love cycling and I love competing. I stopped racing after the 2009 World Championships not because I was burned out, but because my husband and I wanted to start a family,” said Kristin Armstrong. "I told myself from the beginning if everything went smoothly with the birth of our son, Lucas William, I would consider racing again." Armstrong went on to compete on a team she was a part owner of, Peanut Butter & Co. Team TWENTY12.
In 2011, Armstrong did indeed return with Peanut Butter & Co. Team TWENTY12. She won three of the four stages (criterium, road race and time trial) and the overall title during the Sea Otter Classic in April. However, during the first stage of the Tour of the Gila, which she had won twice previously, Armstrong came down with food poisoning. She ended up withdrawing from the race and returning home to recover.
She successfully defended her Olympic title in the individual time trial at the 2012 Olympics in London and became the oldest rider to win an Olympic time trial, and finished 35th in the Women's road race. She announced her retirement after the 2012 Olympics.
In September 2012, Armstrong's Olympic gold medal winning time trial bike was stolen while in transit between Germany and the USA.
In April 2015 Armstrong announced that she would be coming out of retirement to race at the 2015 Pan American Road Championships in Leon, Mexico having been selected by USA Cycling for the individual time trial. However two days after announcing Armstrong's selection the USA Cycling Selection Committee reconvened, deciding that the new selection process under which Armstrong had been chosen had not been published in a timely manner, that as a result the federation's older Principles of Athlete Selection, which had been issued in 2008, should be used for selection to the Pan American Championships, and that Armstrong's place would be taken by Tayler Wiles. The following month Armstrong won the United States National Time Trial Championships in Chattanooga, Tennessee, beating Carmen Small by 13 seconds.
In August 2016, Armstrong made Olympic history in Rio after coming out of retirement to win the gold medal in the women's individual time trial and becoming the first rider ever to win three gold medals in the same discipline.
Armstrong's father was an officer in the US Marines. Born in Memphis, Tennessee, she lived in Tennessee and California and attended high school in Havelock, North Carolina, and abroad in Okinawa, Japan, where she graduated from Kubasaki High School in 1991. She enrolled at the University of Idaho in Moscow, where she ran track for the Vandals for a season as a walk-on and was a member of the Kappa Kappa Gamma sorority. Armstrong earned a bachelor's degree from UI in sports physiology in 1995, and currently lives in Boise, Idaho.
She is often confused with the ex-wife of fellow cyclist Lance Armstrong, whose name is also Kristin. Kristin Armstrong the cyclist and Lance Armstrong are not related.
Armstrong is married to Joe Savola; their son Lucas William Savola was born on September 15, 2010. Four months before his birth, she gave the commencement address at her alma mater in May 2010.