[2] Starting out on two wheels, Harrington won a number of championships and achieved much success in the world of AMA Motocross and Supercross.

He was a multiple race winner in Toyota Formula Atlantic, finishing third in the 1988 championship despite running the uncompetitive Ralt chassis.

Despite failing to qualify for the Indy 500 and suffering serious injuries at Texas 1 (broken left tibia, right fibula, right foot and three ribs) he won the Rookie of the Year honors by a slim margin over Robby McGehee.

In 1998 he was well on his way to a top qualifying position when he suffered a blown engine that ended his month as the team had no backup.

After retiring from active driving, Harrington has achieved success in his driver coaching business,[6] including coaching Highcroft Racing factory Acura team Championship winning owner-driver Duncan Dayton and Mike Miserandino, who has won four national championships in a row.

His latest driver, Jacob Abel, won two of the three F3 Americas races at the Road Atlanta round.