Born in Kentucky, Horn played guard for the 1991 KHSAA state runner-up Tates Creek High School Commodores in Lexington, Kentucky for coach Nolan Barger.
In college, Horn played for Western Kentucky University Hilltoppers in Bowling Green, Kentucky from 1991 to 1995. He was a crowd favorite, hitting a game-winning three-pointer to defeat the University of Louisville on February 16, 1993, in Freedom Hall. While Horn played at WKU, the team made it to the NCAA Tournament three times, defeating Memphis State (led by Anfernee Hardaway) and Seton Hall in 1993 before losing to Florida State University; losing to the University of Texas in the first round in 1994; and defeating the University of Michigan before losing to the University of Kansas (led by Greg Ostertag) in 1995. Horn played for Ralph Willard and Matt Kilcullen while at WKU.
Horn served as an assistant coach from 1995 to 1997 at WKU for then-coach Matt Kilcullen before departing for Morehead State University to serve under Kyle Macy for two seasons before departing for Marquette.
He was an assistant coach at Marquette University under Tom Crean. That Marquette team was led by future NBA players Dwyane Wade and Travis Diener. Crean and Horn first crossed paths when Horn played at WKU and Crean was an assistant for the Hilltoppers under head coach Ralph Willard.
After his tenure at Marquette, Horn was hired as the head coach at Western Kentucky University to replace Dennis Felton, who left for the University of Georgia after three trips to the NCAA Tournament. Prior to his hiring, Travis Diener recommended Horn to the then-WKU athletic director Wood Selig.
Horn compiled a record of 111–48 in five seasons at his alma mater, WKU. He led the Hilltoppers to the Sweet 16, the third round of the 2008 NCAA Men's Basketball Tournament, a tournament run that included one of the most celebrated buzzer beaters in college basketball history, a three-pointer by Ty Rogers against Drake in overtime. Their run ended with a 10-point loss to top-seeded UCLA.
On April 1, 2008, Horn was hired as the new men's coach at the University of South Carolina, replacing Dave Odom.
On March 13, 2012, he was fired as head coach of the Gamecocks after going 60-63 in 4 seasons with only one postseason appearance.
Horn's teams are known for their up-tempo style of play, full-court trapping defense and conditioning. While at WKU, Horn's teams averaged 47% field goal accuracy and averaged approximately 77 points per game.Courtney Lee
Andy Allison - current UMass director of basketball operations
Neill Berry - current High Point assistant coach
Scott Cherry - High Point University Head Coach
Archie Miller - current Indiana University head coach
Chase Richardson - current Troy University assistant coach
William Small - current Iowa State assistant coach
Horn is married to Carla Walker Horn of Franklin, Tennessee. The couple has one daughter, Caroline, and one son, Walker.