Dorn began running as a sophomore at Chattanooga Christian School in 2001, but did not make the varsity team until his junior year. In his junior year, Dorn placed 20th at the TSSAA A-AA Cross Country State Championship Meet with a time of 16:51 for 3 miles. He was the third-place finisher for Chattanooga Christian School and the Chargers finished in 2nd place in the championship. As a senior, Dorn was an All State finisher, running 16:55 for 3 miles and finishing in 14th place. Chattanooga Christian, however, only finished in 4th place at that championship. On the track his senior year, Dorn set a Chattanooga Christian School record for 800 m when he ran 2:03. That record stands today.
After graduating from high school in May 2004, Dorn matriculated to Lee University in Cleveland, TN, where he competed for two years before transferring to Bryan College in Dayton, TN.
In 2005, his sophomore year of college, at the NAIA Region XIII Cross Country Championship meet in Rome, GA, Dorn finished in 26th place, 3rd-place finisher for Lee University, when he ran 32:15 for 8000 m. After a disappointing two years at Lee University, Dorn transferred to Bryan College. In 2006, his first year at Bryan, Dorn was forced to take a medical redshirt after he ripped his Achilles tendon in the first cross country meet of the year. In 2007 he finished in 16th place at the NAIA Region XII Cross Country Championship meet in Elizabethton, TN, the 6th-place finisher for Bryan College, and he ran 27:33 for 8000 m. Bryan won the Region Championship that year and at the NAIA National Championship Meet in Kenosha, WI finished in 27th place. Dorn struggled and finished in 202nd place and was the fourth finisher for Bryan when he ran 27:14 for 8000 m. In 2008, his senior year, Dorn was the only runner from Bryan to qualify for the NAIA National Championship meet, when he finished in 9th place at the Appalachian Athletic Conference Championship Cross Country Meet in Elizabethton, TN. Dorn ran 27:14 for 8000 m at the AAC Championship that year, while Bryan finished in 5th place as a team. At the 2008 NAIA National Championship meet, Dorn again struggled when he finished in 289th place and ran 28:32 for 8000 m.
Dorn qualified for the NAIA Outdoor Track and Field Championships in 2008 as a marathoner. Dorn qualified at the 2008 Scenic City Half Marathon in Chattanooga, TN, when he ran 1:15:44 and finished in 2nd place. However, Dorn was forced to miss the National Championship meet due to a reoccurrence of his previous Achilles tendon injury. The 2009 track and field season, his final semester of collegiate eligibility, brought about many frustrations for Dorn as he repeatedly posted abysmal results. After running 4:55 and 9:42 for one mile and 3000 m indoors, coach Rodney Stoker elected to end Dorn's season, and his college career ended in disappointment.
Andrew Dorn raced one cross country race in 2009, the Southeastern Classic in Louisville, KY where he competed as an unattached athlete and finished in 160th place when he ran 8000 m in 30:00. Dorn's last race as an unattached athlete came on New Year's Eve, when he finished in 7th place at Chattanooga's Karen Lawrence Race for St. Jude's 4 Miler. He ran 22:25 that night, a step towards a return to his old form. In January 2010, Dorn joined the newly formed Team Fast Break, a professional distance running team sponsored by Fast Break Athletics based in Chattanooga, TN. In his first race as a Team Fast Break runner, Dorn finished in third place at the Gateway Bank & Trust 5k road race in Ringgold, GA when he ran 16:27 on March 20, 2010. He made his debut at the 10 mile distance a few weeks later at the Papa John's 10 Miler in Louisville, KY. He finished in 11th place in 56:51 at that race. On October 10, 2010, Dorn competed in his first marathon, the Chicago Marathon, which he completed in 2 hours, 42 minutes, 21 seconds. He raced in Chicago not as part of Team Fast Break, but instead wore a Front Runner Athletics jersey, due to his recently being hired as the store manager at Front Runner Athletics.
In early 2011, Dorn announced that he would race under the Chattanooga Track Club banner, after the club began to seek to sponsor an elite racing team.