First up for Cassill is an attempt to make this weekend's race at Phoenix in a car sponsored by Moon Shine Wildfire Camo. Mike Hillman Sr. will be the crew chief.
Circle Sport, which has an alliance with Richard Childress Racing, is owned by Virginia businessman Joe Falk.
"I'm looking forward to the challenge of helping advance Circle Sport to the next level of competition in the NASCAR Sprint Cup Series," Cassill said. "I have been a part of and understand what it takes for an upstart organization to compete in the Cup Series. They have an established relationship with RCR that I believe will help us, and with the right marketing partners - a company that wants to grow their involvement in the sport - I believe we have just the right opportunity for them with the No. 33 Chevrolet."
Cassill ran all 36 Sprint Cup Series races last year for BK Racing, and Falk said he's paid attention to Cassill's growth.
"I have watched Landon progress as a race car driver, and it was his qualifying efforts in our Cup car in 2010 and 2011 that caught the eye of James Finch and earned him his first big break in NASCAR's premier series," Falk said. "Landon has a tremendous amount of potential and we believe we're building a program that will allow him to showcase his talents."