[3] He began working in entertainment when he was 12 years old, when he was put in charge of his father's props for shows, including his harp.
He continued his work on films outside the horror genre throughout the 1980s, such as arranging music for John Cassavetes' Big Trouble.
[4] In the late 1980s, Marx and harpist Carrol McLaughlin toured the United States, giving performances and promoting Harpo Speaks, his father's autobiography.
[12] In the early 1990s, Los Angeles magazine named Marx the most popular lounge pianist in that city.
[13] As of December 2019[update], Marx was still playing as a lounge pianist in and around Palm Springs and Rancho Mirage.