[4] Carr is credited with the lyrics and music for the song,[4] which uses a departed train as a metaphor for a lover who has left: Heard the whistle blowin', couldn't see no train Way down in my heart, I had an achin' pain How long, how long, baby how long Carr's and Blackwell's songs reflected a more urban and sophisticated blues, in contrast to the music of rural bluesmen of the time.

[5] Carr's blues were "expressive and evocative",[6] although his vocals have also been described as emotionally detached, high-pitched and smooth, with clear diction.

"How Long, How Long Blues" became an early blues standard and "its lilting melody inspired hundreds of later compositions",[1] including the Mississippi Sheiks' "Sitting on Top of the World" and Robert Johnson's "Come On in My Kitchen".

[8] Although his later style would not suggest it, Muddy Waters recalled that it was the first song he learned to play "off the Leroy Carr record".

"[8] In 2012, the song received a Grammy Hall of Fame Award, which "honor[s] recordings of lasting qualitative or historical significance".