After studying music under New York University professor Orville Mayhood and then under the influential Joseph Schillinger, he was invited to join the arrangers' roster for the popular Hal Kemp Orchestra, alongside John Scott Trotter (who was about to leave the band) and Lou Busch.
On his return from the war, Mooney became a freelance arranger in Hollywood and started to make a name for himself, providing charts for top vocalists such as Bing Crosby, Frank Sinatra, Judy Garland, Peggy Lee, Kay Starr, and Billy Eckstine.
There, he provided arrangements for more top singers, including Sarah Vaughan, Dinah Washington, Helen Merrill, Ernestine Anderson and, on Mercury's parent label Philips Records, Nina Simone.
Though those arrangements grated with some jazz purists, their dramatic qualities inspired the acclaimed singer to some of her finest work, for example Hit Shows' "It Never Entered My Mind" [1] and the Gershwin album's Isn't It a Pity?.
Mooney's numerous arrangements for Dinah Washington, meanwhile, ranged from straight big band swing, through Latin mambo to rhythm and blues, but the seven albums on which he worked with Simone, between 1964 and 1967, display the greatest versatility.
Philips decided to phase out the Mercury label in the late 1960s and so Mooney moved on to Universal Studios, where he became musical director on many of the most popular TV shows of the 1970s, including Columbo, Kojak, Marcus Welby, M.D., Ellery Queen, The Six Million Dollar Man, The Bionic Woman, Kolchak: The Night Stalker and The Rockford Files.