He studied with Nadia Boulanger when stationed in Paris and then under William Walton at Trinity College of Music in London.

He played in Lester Lanin's band at this time and found work as an accompanist for singers such as Judy Garland, Maurice Chevalier, and Marlene Dietrich.

[4] In 1962, he was hurt in a car crash, and while he recovered, Kapp Records asked him to work on writing potential hits in the then-hot genre of bossa nova.

Often at the end of a show Shore would gather round Harnell at the piano and she and her guests that evening would make requests of him for a song they wanted to sing.

[3] In 1973, Harnell moved to Hollywood and worked in film score and television composition, composing for The Bionic Woman, The Incredible Hulk,[4] including "The Lonely Man Theme" with which all episodes of The Incredible Hulk ended, playing over David Bruce Banner walking down yet another lonely road, Alien Nation, and V, for which he received an Emmy nomination in 1983.

[5] His son, Jess Harnell, is a voice actor and singer, best known as the voice of Wakko Warner on the Steven Spielberg-produced animated television series Animaniacs,[6] Crash Bandicoot in the Crash Bandicoot franchise, and the announcer of America's Funniest Home Videos, which he has announced since 1998.