Miller began his career at the age of 12 in kart racing in the Junior Shifter Kart Association, winning the Grand National championship three times. In 1998, he won the U.S. Nationals while competing in various parts of the world. He would eventually be inducted into the Hall of Champions in San Diego and was named San Diego's "Amateur Athlete of the Month." He began racing stock cars the following season at Irwindale Speedway. In his second year competing, he won four races and twelve top-fives. He then moved to Mesa Marin Raceway and won the track championship in 2002.
In 2005, Miller was hired to drive the No. 21 Reese'sChevrolet Monte Carlo in the Busch Series for twelve races, sharing the ride with Kevin Harvick. Miller posted two top-ten finishes over the course of the season and finished 48th in the final standings. Harvick's decision to run the full Busch schedule in 2006 forced Miller out of a permanent position with RCR. He remained with the team as a fabricator and test driver, occasionally practicing and qualifying race cars for the team as necessary. He spent 2007 driving the No. 40 Westerman Companies Chevrolet for Curtis Key.