In 2004, Bowyer shared seat time in the #21 Reese's Chevrolet with Kevin Harvick, driving in half of the 34 races that year. He had 1 pole and 7 top tens, and attained a season-high 3rd place finish in the Federated Auto Parts 300, a Nashville Superspeedway race in June.
Bowyer's first full season was in 2005, replacing Ron Hornaday in the #2 ACDelco Chevrolet. He had a fine year, winning two poles and two races en route to a second place finish to repeat-champion Martin Truex Jr., losing only by 68 points. Bowyer has continued to race full-time in the 2006 Busch Series season, along with being a NEXTEL Cup regular.
Bowyer made his NEXTEL Cup (now Sprint Cup) debut in the Sylvania-sponsored #33 Chevy on April 23, 2005, during the Subway Fresh 500 at Phoenix International Raceway. He finished 22nd as the first car one lap down. During his successful season in the Busch Series, Richard Childress Racing announced on October 15, 2005, that Clint Bowyer would race the #07 Chevrolet full time in the NEXTEL Cup series, replacing Dave Blaney in the 2006 season.
In his second NEXTEL Cup race, Bowyer finished 6th in the 2006 Daytona 500, and followed it up by placing 14th the next week. He began to struggle through the next several races, averaging a 22nd place finish and falling out of the top-ten in the points standings, but rebounded in the Subway Fresh 500; he led 21 laps and eventually finished fifth. He is currently 16th in the standings, and is second to Denny Hamlin in the Rookie of the Year race by 44 points.In 2007 Bowyer finished 18th in the Daytona 500 after he slid across the finish line upside down and on fire following a big crash started by Kyle Busch.After barley making the Chase,he scored his first win in the Sylvania 300 at New Hampshire. This and other strong runs help[ed him finish 3rd in the standings behind Jeff Gordon and seris champion Jimmie Johnson.2008 saw another good year for Bowyer who got his second win in the Dan Lowry 400 at Richmond and finished 5th in points.It was announced that Casey Mears would piolt the 07 and Bowyer would move to the team's new 33 car.