Dillon competed in the Sprint Cup Series on a limited basis in 2012, starting at Michigan International Speedway in June, driving the No. 33 Chevrolet for Richard Childress Racing, starting 21st and finishing 24th.
On June 29, 2012, Dillon recorded his first Nationwide Series win at Kentucky Speedway; he dominated the race by leading all but 8 laps and won by over 9.8 seconds over second place. However, NASCAR officials announced the car had failed post-race inspection because the rear ride heights were too low.
Dillon also participated in one race in the NASCAR Canadian Tire Series at Circuit Gilles-Villeuneuve in Montreal in August 2012. Dillon finished 7th while driving the No. 4 car for Fitzpatrick Motorsports.
Dillon announced in August 2012 that he would continue to drive full-time in the Nationwide Series for 2013, with Advocare as the primary sponsor for the full season, along with running seven Sprint Cup Series races that year, including the 2013 Daytona 500, where he qualified 8th, but crashed late in the race, relegating him to a 31st-place finish. In January 2013 it was announced that some of Dillon's Sprint Cup races that season would be in Phoenix Racing's No. 51 Chevrolet.