Horton began gymnastics at the age of four in 1990. “I was a wild child”, Horton said, “I once climbed a pole in the middle of Target all the way to the ceiling. I used to do back flips on my parents’ bed and I rode a garage door to the top when I was 3 years old.”
Horton made his debut as a senior (despite still competing as a junior) in 2002 competing at the U.S. National Championships in Cleveland, Ohio where he placed first on rings and vault, placed second in the all-around and the floor exercise, and tied for fifth on the high bar. In 2003 he competed in the Winter Cup challenge, where he qualified to the individual event finals. Later that year he was chosen to compete for US at the Pan American Games in Santo Domingo where the men’s team won bronze and he placed fourth all-around.
He competed in both the U.S. Nationals and the Olympic Team trials in 2004, where he placed 13th. The same year he entered the University of Oklahoma. He was recruited by Iowa, Michigan, Ohio State, Oklahoma and Penn State and committed to compete for the University of Oklahoma beginning in 2004 for the 2004–05 NCAA season.
From 2005–08 he competed for the Oklahoma Sooners gymnastics team alongside his 2010 & 2011 world teammates Chris Brooks and Steven Legendre. During his time competing for Oklahoma he won 6 NCAA titles and 18 All-American honors, breaking the record that had previously been set by Bart Conner. His OU record for titles and honors still stands.
In 2005, he once again competed at the Winter Cup, placing eighth all-around and was selected again for the U.S. National Team.
At the beginning of 2006, during his Second year at OU, he won an all-around silver at the Winter Cup. He went on to compete at the American Cup where he won the all-around and rings competitions. That summer, he competed in the U.S. National Championships where he won gold on the floor, silver in the all-around and bronze on the horizontal bar. His performances led to him being chosen to represent the U.S.A. at the 2006 World Artistic Gymnastics Championships in Aarhus. A very young and inexperienced worlds team, they finished 13th in the qualifying rounds not making the team finals.
In 2007 he competed at the Winter Cup and the American Cup again. He won his second consecutive American Cup All-Around title, the first male gymnast to do so since Blaine Wilson. After competing in the NCAA and U.S. National Championships he was once again chosen for the 2007 World Artistic Gymnastics Championships, where he finished fourth in the all-around and helped the U.S.A. qualify a full men’s team to the 2008 Summer Olympics.
In 2008 he competed in Winter Cup, the American Cup as well as competing as a Senior for Oklahoma. That year the Sooners won the NCAA Championships, and Horton won another NCAA individual title on the rings. At the U.S. National Championships in Houston, Horton won silver medals on the floor, rings and all-around. This qualified him to the 2008 U.S. Olympic Trials.
Horton was named to the U.S. Olympic team following the 2008 Olympic Trials, where he was the all-around champion. The team entered the 2008 Beijing Olympics amongst much skepticism as to whether the team could compete against such established teams as the Japanese, Chinese, and German teams. Injuries had forced team leaders Paul Hamm and Morgan Hamm to withdraw from competition, causing the American team to bring in alternates Raj Bhavsar and Alexander Artemev. The American men performed better than anticipated, with Horton being the team’s top performer. The American team ended the competition with the bronze medal after a stressful pommel horse event. In the event finals, Horton placed ninth all-around and added a silver medal in the high bar event.
In 2009, Horton became the U.S. National Champion, and went on to compete in the 2009 World Artistic Gymnastics Championships in London where he reached the finals in the all-around and on the horizontal bar.
In 2010, he competed in the American Cup where he placed second all-around. That summer he defended his national all-around title at the U.S. National Championships in Hartford. He was selected for the 2010 World Artistic Gymnastics Championships in Rotterdam, where the U.S. team placed fourth, and Horton won the all-around bronze medal.
In 2011 he won his third American Cup all-around title, and was captain of the U.S. team that won the bronze medal at the 2011 World Artistic Gymnastics Championships. Although qualifying fifth all-around in the preliminary round, he was edged out by teammates Danell Leyva and John Orozco (only two athletes from each country were allowed to compete in individual event finals). Regarding this he said “I didn’t make the all-around final because two of my teammates are freakin’ awesome at gymnastics – but it doesn’t matter, because I’m all about the team”. During the team final, he had a bad landing on vault, injuring his left foot, but continued to compete. The next day he was unable to walk, yet after treatment competed on the rings. On returning home, it was discovered that the injury was worse than previously thought, with a torn ligament and broken two bones in a foot that would require surgery. Despite this setback in his training, he told media that it could actually make him stronger gymnast because ‘[he would] have an opportunity to get really strong on the other four events.’
In 2012 Horton qualified for the men’s artistic gymnastic 2012 London Olympic team. The New York Times stated that the team roster was “considered so good that it could be the first United States men’s team to win gold since the 1984 Los Angeles Games.” The team finished fifth, while Horton’s best result was sixth place on the horizontal bar.