After touring with the Norman Luboff Choir, he took a job with an Omaha, Nebraska, advertising agency writing jingles. These included spots for a local bakery featuring the fictional trucker C. W. McCall. The spots were co-written with the advertising writer William Fries, who became the voice of McCall. The spots were so popular that they were persuaded to begin writing non-advertising songs featuring McCall. The duo released five albums between 1974 and 1979. Davis was named SESAC Country Music Writer of the Year in 1976.
Davis founded Mannheim Steamroller in 1974 to showcase his interest in fusing modern popular and classical techniques. The first album, Fresh Aire, was completed shortly after. It was turned down by major record labels so Davis founded American Gramaphone to release it. American Gramaphone has been the label for all subsequent Mannheim Steamroller releases. Eight Fresh Aire albums were released, concluding with Fresh Aire 8 in 2000.
Mannheim Steamroller released Mannheim Steamroller Christmas in 1984; Davis is credited with revolutionizing the "traditional" sounds of Christmas. The group's subsequent Christmas music albums have sold tens of millions of copies and become among the most popular recordings in that genre. His annual Mannheim Steamroller Christmas concert tour, utilizing two cover bands which tour simultaneously, has continued for over 25 years across the US. Davis was awarded his 19th Gold Record in 2010. The Recording Industry Association of America has also awarded Davis four Multi-Platinum and eight Platinum records.