Born as the eldest in an orphaned family, Moore worked as a stevedore and construction worker in the late thirties and early forties. He began performing in bars located in Baton Rouge under the name Harmonica Slim. He Later accompanied Lightnin ' Slim, his brother-in-law, both live and in the studio before his solo career began in 1957. James Moore, now called as Slim Harpo by producer Jay Miller, made his debut single "I'm a King Bee and I Got Love If You Want It (b-side), influenced by Jimmy Reed. He began recording under the Excello Records record label and made notable R & Bsingles -combined with his vocals and harmonica. A few of those notable singles were: "Rainin' In My Heart" (1961), "I Love The Life I Live", "Buzzin'" (Instrumental) and "Little Queen Bee" (1964).
Harpo was known for his harmonica, the name "Slim Harpo" was a humorous substitute for "slim harp", a popular nickname for the harmonica that was used in the blues world.
Harpo's relaxed, almost lazy Act put his style down. Its warm and slow voice was good to hear on the single "I'm a King Bee", which The Rolling Stones recorded later. ZZ Top and The Rolling Stones also covered his song "Shake your Hips", originally recorded by Harpo in 1966. Also, the Pretty Things, the Yardbirds, The Kinks and have Them Harpo song (s) played "peaceful easy feeling". In 1966 Harpo US Top 20 pop hit "a hit with the song" Baby Scratch My Back ", which is also a # 1 R & B hit was and what revitalized his career. Harpo was not a full-time musician, in addition to blues artist he was also owner of a truck company in the sixties.