Marx began his career in music at the age of 5, singing commercial jingles written by his father; Dick Marx's list of "commercial" hits includes Arm & Hammer and Nestlé Crunch.

Marx was 17 and living in Highland Park, Illinois when a tape of his songs ended up in the hands of Lionel Richie. Richie said he thought Marx had the talent to make it big, saying "I can't promise you anything, but you should come to L.A." So after graduating from high school, Marx moved to Los Angeles and visited Richie. Marx contributed backing vocals to Richie’s hits "You Are", "Running with the Night", and the chart-topping "All Night Long", on Lionel's follow-up album.

In those early years, Marx would find any excuse possible to labour in the recording industry. His enthusiasm and his presence in the studio landed him several jobs as a background singer for artists like Madonna and Whitney Houston, and, eventually, as a songwriter. While working as a songwriter and doing background vocals, Marx continued to pursue a record deal of his own. His demo tape was rejected by every label in Hollywood until, finally, four years after moving to Los Angeles, the president of EMI/Manhattan Records, Bruce Lundvall, heard Marx's demo and knew he had a star on his hands. He gave Marx a record deal and Marx created a ten-track album that put him on the path to success.

Marx's self-titled debut album, released in June 1987, yielded four hit singles and sold nearly 4 million copies in the US. The debut single, "Don’t Mean Nothing", had been released the previous month and climbed to #3 on the Billboard Hot 100 as well as #1 on Billboard's Album Rock charts. Marx became the first new artist played on 117 radio stations nationwide during his initial week on the charts. The next two singles, "Should’ve Known Better" and "Endless Summer Nights", reached #3 and #2, respectively. The fourth single release, "Hold on to the Nights", earned Marx his first #1 single.

With the success of his self-titled album, Marx became the first male artist to reach the Top 3 with four singles from a debut album. In 1988, Marx was nominated for a Grammy Award for 'Best Rock Vocal Performance - Male' for "Don’t Mean Nothing".

Repeat Offender, Marx’s second release (May 1989) hit pole position and pushed Prince out of the #1 spot on Billboard's Album chart. It went triple platinum within a few months and eventually sold over 5 million US copies. The first two singles, "Satisfied" and the platinum-selling "Right Here Waiting," both reached #1, completing a string of three consecutive No. 1 singles. When the third single from Repeat Offender, "Angelia" climbed to #4, Marx became the first solo artist to reach the Top 5 with his first seven singles.

Marx also received his second Grammy nomination in 1990 for "Best Pop Vocal Performance - Male" for “Right Here Waiting”.

Marx went on to release a number of other albums. In 1991 he released his third consecutive multi-platinum album Rush Street. "Hazard", which depicted a man being wrongfully accused of murder in a fictional version of Hazard, Nebraska, went #1 in charts around the world.