Al Unser III is the son of 2-time Indianapolis 500 race winner Al Unser, Jr., grandson of 4-time winner Al Unser, and grandnephew of 3-time winner Bobby Unser.

Unser began driving go karts at age 10, but stopped racing until after earning his driver's license at 16. After attending driving schools, Unser competed in the Skip Barber Western Racing Series in 2002, winning six races and earning "Rookie of the Year" honors. A year later, he posted four top-10 finishes in the Barber Dodge Series. In 2004, Unser made his Toyota Atlantic Championship debut, running in four of the 12 series events. His best finish came in his final start of the season when he was eighth at Montreal's Circuit Gilles Villeneuve. He also ran in eight of twelve races in the Infiniti Pro Series, a feeder series to the Indy Racing League, and finished third five times. Unser started the 2005 season in the Infiniti Pro Series, posting three top-10 finishes in the first four races. He then returned to the Toyota Atlantic series and finished the season 7th in championship, after running ten of twelve events and posting a best finish of 4th. In 2006 he drove in 2 Champ Car Atlantic series events with a best finish of 19th and went on to compete in teh Indy Lights Series, then Indy Pro Series through 2008.