Mooney's first job, at age 12, was playing the piano for requests called in to a local radio station.

They continued performing together on WLW in Cincinnati until 1936, after which time Dan Mooney left the music industry.

In 1937, Mooney began working as a pianist and arranger for Frank Dailey,[3]: 505  a role he reprised with Buddy Rogers in 1938.

Through the early 1940s he arranged for Paul Whiteman,[3]: 453  Vincent Lopez, Larry Clinton,[3] Les Brown, and The Modernaires.

'"[4] As for Mooney himself, the columnist wrote that he "played in virtuoso fashion ... a fellow who knows not only his instrument, but jazz music, both to just about the ultimate degree.