David Ragan made his Truck Series debut at the age of 18 at Texas for Fiddleback Racing where he finished twentieth. Ragan ran nine more races that year, with his best finish being nineteenth. In 2005, Ragan was also a contender on the TV series Roush Racing: Driver X. Despite concerns from Roush executives about Ragan being outspoken, he won a ride in the Truck Series. In 2006, Roush had intended for Mark Martin and Ragan to split duties in the No. 6 Ford F-150. Ragan would end up running the No. 50 Ford in several races that Martin was scheduled to run.

Ragan would begin to struggle, crashing twice and never finishing on the lead lap in four starts. Ragan would go on to collect his first top ten at Texas, finishing eighth. Ragan's first pole in a truck would come at Indianapolis.

Ragan made his first Nationwide Series start at California, where he replaced Danny O'Quinn in the No. 50 Ford Fusion. That year his best finish would be a disappointing thirty-sixth place.

In 2006, Roush Fenway Racing named Ragan as the full time driver for the No. 6 Cup entry in 2007, replacing the long-time driver Mark Martin. Ragan assembled a fifth place finish at the season opener at Daytona. Ragan finished third at Richmond, his highest finish to date. Ragan concluded the 2007 season with a runner-up finish to Juan Pablo Montoya in the Raybestos Rookie of the Year standings.

In his sophomore season Ragan made a tremendous improvement collecting six top-5 and 14 top-10 finishes en route to a 13th place finish in the point standings, finishing the highest among non-chase contenders.